The Plate Number Coil Catalog™ uses a numbering system specifically developed to accommodate the unique categorization requirements within the philatelic specialty of plate number coil (PNC) collecting. The numbering system was also designed to minimize PNC collectors’ reliance on the memorization of an extensive list of catalog numbers that have no meaningful relationships to the stamps they represent. The PNC Catalog Numbering System achieves these goals by assigning to each PNC a unique alphanumeric designation that is comprised of the following components:

• Series or Set Identifier — a single, capitalized letter that represents the series or set to which the stamp belongs

• Denomination Identifier — numeric representation of the stamp’s denomination

• Design Identifier — a mnemonic code of one or more letters that relates to the stamp’s design (if required to differentiate a stamp from another stamp with the same denomination but a different design)

• Production/Variety Identifier — mnemonic code that relates to a major production variety (if required to differentiate a stamp from another stamp with a similar design except for the noted production variety)

• Adhesive Type Identifier — a code that represents the primary category of adhesive on a stamp (if required to differentiate a stamp from another stamp with the same design but a different adhesive type)

• Separator — a hyphen, which acts as a separator between the primary components of a PNC Catalog Number and the plate number

• Plate Number — the plate number, sleeve number, or cylinder combination

• Tagging Type Identifier — a two or three character code that identifies the type of phosphorescent tagging present on a stamp (if required to differentiate a stamp from a similar stamp with different tagging)

• Precancel Identifier — an alphabetic code to identify precancel types (if applicable)

The following sections describe each of these components and provide examples of its use within the context of an actual PNC Catalog Number.

Series or Set Identifier

Each PNC Catalog Number starts with a single, capitalized letter that represents the series or set to which the stamp belongs. The series or sets described in The Plate Number Coil Catalog are listed below with the corresponding representative letters that are used in the PNC Catalog Numbering System.

• Flag Coil Stamps — F
  The Flag Coil Stamps category includes coil stamps that have been issued since 1981 that feature the United States flag.

• Transportation Series Stamps — T
  The Transportation Series Stamps category includes all stamps from the Transportation Series.

• Regular Coil Stamps — R
  The Regular Coil Stamps category includes coil stamps with plate numbers that have been issued with whole-cent denominations for general postage use such as first-class letter rates, additional ounce rates, and postcard rates.

• Service-inscribed Coil Stamps — S
  The Service-inscribed Coil Stamps category contains coil stamps with plate numbers that have been issued with a specific mail class (such as “Bulk Rate” or “Presorted First-Class”) included in the stamp’s design.

• Contingency Coil Stamps — C
  The Contingency Coil Stamps category features the non-denominated coil stamps that were issued to meet postal needs during first-class letter rate changes.

• Philatelic Self-adhesive Coil Stamps — P
  The Philatelic Self-adhesive Coil Stamps category includes self-adhesive coil stamps with plate numbers that have been issued specifically for philatelic purposes and were not generally available to the public.

• Variable Denomination Coil Stamps — V
  The Variable Denomination Coil Stamps category has coil stamps with plate numbers that were dispensed from machines that printed a customer-selected denomination at the time of each purchase.

• Official Coil Stamps — O
  The Official Coil Stamps category includes all of the coil stamps bearing plate numbers that have been issued for official (U.S. government) use.

• Test Coil Stamps — X
  The Test Coil Stamps category includes coil stamps with plate numbers that were produced specifically for testing coil vending machinery and have no postage value.

These series or sets collectively form a comprehensive, primary categorization for all PNCs. The list of stamps included in some of these categories will remain mostly static—such as those included in the Transportation Series Stamps and the Philatelic Self-adhesive Coil Stamps categories; however, other categories will continue to grow as new stamps are issued and new plate numbers are produced. If new coil stamp series or sets are defined and supported by the USPS, additional categories can be added and be represented by different letters.

The following four examples show PNC Catalog Numbers from the Flag Coil Stamps and Transportation Series Stamps categories:

• F18-1

• F20-1

• T18-1

• T25-2

The “F” in the first two examples identifies them as part of the Flag Coil Stamps category. Specifically, F18-1 is the 18¢ Flag “…from sea to shining sea” coil stamp from sleeve 1; and F20-1 is the 20¢ Flag over the Supreme Court coil stamp from sleeve 1. Similarly, the “T” in the third and fourth examples identifies these numbers as part of the Transportation Series Stamps category. The T18-1 number represents the 18¢ Surrey coil stamp from plate 1, and the T25-2 number represents the 25¢ Bread Wagon coil stamp from sleeve 2.

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Denomination Identifier

The series or set identifier in a PNC Catalog Number is followed by the stamp's denomination. The denomination is the postage value that appears in the printed stamp design; or in the case of non-denominated stamps, the selling value assigned by the USPS. (Test stamps, which do not have a postage value, do not include a denomination identifier in their PNC Catalog Numbers.) The following guidelines are used in noting a stamp's denomination in the catalog number:

• Denominations of whole cents that are less than 10¢ are represented by a single digit (1 through 9, inclusive) even if a leading 0 (zero) appears in the stamp's printed denomination.

• Denominations of whole cents that are 10¢ or greater, but are less than $1.00, are represented by a two-digit number (10 through 99, inclusive).

• Fractional denominations—denominations that are less than $1.00, and include fractions (tenths) of a cent—are represented by the whole-cent number followed by a decimal point and then the single digit noting the tenths of a cent (for example, 10.9).

• Denominations of whole-dollar amounts are represented by the dollar sign ($) followed by the whole number (for example, $1.00 is represented by $1).

The following four examples show PNC Catalog Numbers from the Flag Coil Stamps and Transportation Series Stamps categories that illustrate the above guidelines:

• F18-1

• T1-1

• T9.3-1

• T$1-1

With an understanding that the “F” in the first example above identifies it as part of the Flag Coil Stamps category, the “18” that follows the “F” identifies the specific denomination of the stamp from within the category. Following the previously stated guidelines for a two-digit denomination, the “18” translates to 18¢. When combined, the “F18” uniquely denotes the 18¢ Flag“…from sea to shining sea” coil stamp. The “-1” completes the PNC Catalog Number by showing the sleeve number—which is 1.

The other three examples each begin with “T,” which identifies each of them as part of the Transportation Series Stamps category.

In the first of these, the “T” is followed by “1.” Following the guidelines for a single-digit denomination, the “1” represents 1¢. The “T1” of the example signifies the 1¢ stamp of the Transportation Series Stamps—the 1¢ Omnibus. The “-1” again completes the PNC Catalog Number by showing the plate number. Thus, “T1-1” is the PNC Catalog Number for the 1¢ Omnibus from plate 1.

The second example from the Transportation Series Stamp has a “9.3” denomination. The period (.) between the digits acts as a decimal point, which equates the denomination identifier to 9.3¢. The “T” and the “9.3,” therefore, combine to identify the 9.3¢ Mail Wagon coil stamp from the Transportation Series Stamps. As in the previous examples, the “-1” completes the PNC Catalog Number by showing the plate number. Hence, “T9.3-1” is the PNC Catalog Number for the 9.3¢ Mail Wagon coil stamp from plate 1.

The last Transportation Series Stamp example from above shows “$1” after the “T.” In this example, the dollar sign ($) and the “1” represents a denomination of $1.00. Collectively, the “T” and the “$1” identify the $1.00 Seaplane coil stamp from the Transportation Series Stamps. Following the pattern, the “-1” completes the PNC Catalog Number for the $1.00 Seaplane coil stamp printed from sleeve 1.

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Design Identifier

When a denomination exists on more than one design within the same series or set, one or more alphabetic characters are added to the right of the denomination in a PNC Catalog Numbers to ensure clarity. These characters directly relate to the subject of the stamp, and preferably are the initial letters of the words appearing on the stamp. These letters provide distinctive PNC Catalog Numbers and also act as a mnemonic device aiding in the recollection of which PNC Catalog Number represents which stamp.

The following examples illustrate this technique for the design-different 5¢ stamps of the Transportation Series:

• For the 5c Motorcycle — T5M

• For the 5c Milk Wagon — T5MW

• For the 5c Circus Wagon — T5CW

• For the 5c Canoe — T5C

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Production/Variety Identifier

Some PNCs require a production/variety identifier in their PNC Catalog Numbers to distinguish them from varieties of the same basic design. These varieties occur because of press changes, minor design modifications, or processing changes. When required, a production/variety identifier consists of a mnemonic code enclosed in parentheses that appears to the right of the series or set, denomination, and design identifier components in a PNC Catalog Number. Descriptions and examples of the different production/variety identifiers are provided below. 

When a coil stamp design was printed on more than one press and the adhesive type identifier, the plate number, or the tagging type identifier components of the associated PNC Catalog Numbers do not distinguish the different press varieties, a production/variety identifier denoting the press that produced each variety needs to be included in the respective PNC Catalog Numbers. To date, production/variety identifiers relating to press changes are only required in some PNCs produced by the Bureau of Engraving and Printing (BEP). Because the BEP generally assigns a letter as an informal designation to each of its presses, these letters are used to form the production/variety identifiers to denote the presses that printed particular PNC varieties.

In the special cases where the BEP moved the production of six Transportation Series coils from the aging Cottrell presses to the newer B press (also referred to as press 701), a capitalized B enclosed in parentheses follows the denomination or the mnemonic identifier. In each case, the B-press version of the stamp had a distinctly different printed image from a stamp that was previously issued with a similar design bearing the same denomination and was produced using the same printing method (such as intaglio). The Cottrell presses and B press also used different printing surface configurations that affected the features of the printed coils. The Cottrell presses used two semi-circular curved plates that formed a cylindrical surface when joined on the press. The edges of the two semi-circular plates butting together caused a vertical joint line to be printed between the numbered stamp of a coil and the stamp to its right. The two, paired plates also had unique plate numbers, which caused the plate numbers to alternate every 24 stamps (the width of each plate). In contrast, the B press used a single cylindrical printing sleeve. Therefore, coil stamps printed from this press did not exhibit joint lines and only had one plate number that repeated at intervals equal to the circumference of the printing sleeve, which was 52 stamps.

The following examples show the PNC Catalog Numbers (without the sleeve numbers) for the B-press versions of the affected stamps:

• For the 1c Omnibus — T1(B)

• For the 2c Locomotive — T2(B)

• For the 4c Stagecoach — T4S(B)

• For the 8.3c Ambulance — T8.3(B)

• For the 12c Stanley Steamer — T12(B)

• For the 14c Ice Boat — T14(B)

In 1988, press and production schedules precluded the BEP from exclusively using the combined offset/intaglio capabilities of the D (902) press to print the 25¢ Honeybee coil stamp. As a result, the BEP printed some of the 25¢ Honeybee coil stamps on the combination D press, but the rest of the production was completed by first printing the offset portion of the design on their Optiforma (043) press and then later feeding the same web into the C (901) press to print the black intaglio portion of the design.

To represent the distinctive products from each of these printing processes for the 25¢ Honeybee, production/variety identifiers denoting the presses are used in the Honeybee’s PNC Catalog Numbers. Using a “D” to represent the D press printing and an “O/C” to represent the multi-press printing process utilizing the Optiforma press and the C press, the following distinctive PNC Catalog Numbers are derived (shown in chronological order from earliest to latest):

• R25H(O/C)-1 (exists with full-height and cut plate number 1)

• R25H(D)-1

• R25H(O/C)-2

• R25H(D)-2

In later efforts to efficiently employ available printing equipment to meet production needs, the BEP used three different presses to produce three unique versions of the 1¢ American Kestrel coil stamp. Oddly, the original printing of each version displayed the same 4-digit printed cylinder combination (plate number) of 1111—even though each version used a different set of printing cylinders. Although each press used offset printing to produce the stamp images and have the same 4-digit cylinder combination, PNCs from each press have distinctive, collectible characteristics—which, in turn, require distinctive PNC Catalog Numbers. Kestrel coil stamps from each of the presses vary slightly in color (predominantly in the tan background), but the most distinctive characteristic is found in the order (left to right) of the colors of each of the digits in the printed cylinder combination. Because of differences between the presses, the four colors that combine to produce the Kestrel design had to be applied in different orders to ensure the highest quality printed image from each press.

To ensure clarity, the PNC Catalog Number for each of the varieties includes a 4-character production/variety identifier enclosed in parentheses following the design identifier. Each of the production/variety identifiers uses “B” for black, “Y” for yellow, “C” for cyan, and “M” for magenta to represent the four ink colors in the order that they appear in the printed cylinder combination. Therefore, the PNC Catalog Number for each variety is as follows (presented in chronological order of production from earliest to latest):

• R1K(BYCM)-1111 — was printed on the offset stations of the BEP’s offset/ intaglio combination D (902) press. Reading from left to right, the order of the colors in the cylinder combination is Black, Yellow, Cyan, and Magenta.

• R1K(BCYM)-1111 — was printed on the BEP’s 4-color Optiforma (043) press. Reading from left to right, the order of the colors in the cylinder combination is Black, Cyan, Yellow, and Magenta.

• R1K(YMCB)-1111 — was printed on the offset stations of the BEP’s offset/ intaglio combination F (801) press. Reading from left to right, the order of the colors in the cylinder combination is Yellow, Magenta, Cyan, and Black.

Repeated use of the non-denominated (10¢) Eagle and Shield design for several distinct postal coil issues required the introduction of another production/variety identifier. Originally, the (10¢) Eagle and Shield design was issued as a coil stamp with water-activated gum and a “Bulk Rate” service inscription. Three different vendors—American Banknote (ABN), the Bureau of Engraving and Printing (BEP), and Stamp Venturers (SV)—produced three different versions of this stamp with differences in the service inscription wording and the colors of inks that were used.

After the USPS instituted a policy to incorporate the year-of-issue dates on all stamps, the (10¢) Eagle and Shield design was issued in a new format—pressure sensitive adhesive with spaces—that included a 1996 year-of-issue date in the lower left corner of the stamp’s design.

In 1998, the USPS again used the Eagle and Shield design for another coil issue. The design, however, was modified to reflect the updated terminology in the USPS rate structure, which changed the service inscription from “USA Bulk Rate” to “USA Presorted Std.” The design also included the proper year-of–issue date (1998) for the new issue. The “Presorted Std” design was printed by the BEP in two formats—3,000- and 10,000-stamp coils with water-activated gum and in 10,000-stamp coils with pressure sensitive adhesive with spaces.

To properly segregate the six varieties of the Eagle and Shield design, a distinctive production/variety identifier is included in the PNC Catalog Number for each of the last three issues. For these stamps, the production/variety identifier is a 2-digit representation of the year-of-issue date that is shown on the individual stamps. Like other production/variety identifiers in the PNC Catalog Numbering System, the digits are enclosed in parentheses after the design identifier component.

The following list includes examples of PNC Catalog Numbers for each coil issue with the basic (10¢) Eagle and Shield design:

• S10ES-A11111 (41 total cylinder combinations produced by ABN)

• S10ES-11111 (4 total cylinder combinations produced by BEP)

• S10ES-S11111 (2 total cylinder combinations produced by SV)

• S10ES(96)[psa]-S11111 (1 cylinder combination produced by SV)

• S10ES(98)[psa]-11111 (3 total cylinder combinations produced by BEP)

• S10ES(98)wag-11111 (2 total cylinder combinations produced by BEP)

During a period between late 1985 and 1991, the 21.1¢ Letters issue and stamps featuring four different stamp designs from the Transportation Series marked an evolution in USPS policies that resulted in the elimination of overprinted precancels in favor of service-inscribed stamps. They also marked an end to the issuance of tagged versions of the designs used for precanceled and/or service-inscribed stamps issued to meet discounted postal rates. The four Transportation Series designs are the 5.5¢ Star Rout Truck, the 7.1¢ Tractor, the 11¢ Caboose, and the 17.5¢ Racing Car.

Collectively, the stamps issued with these designs stand apart from other PNCs because they include untagged, service-inscribed stamps without overprinted precancels and tagged versions of the same basic designs that were printed from different printing sleeves without the service inscriptions. These distinctive characteristics make it necessary for a production/variety identifier to be included in the PNC Catalog Numbers for the service-inscribed versions of these designs.

Because this production/variety identifier denotes the PNCs associated with these issues as service-inscribed stamps, the identifier consists of a “si” enclosed in parentheses. However, one of these designs exists with two different service inscriptions. To accommodate this distinction, the identifiers for the two PNC Catalog Numbers are extended to describe the individual service inscription. This only occurs on the 7.1¢ Tractor coil stamp, which was issued in February 1987 with a “Nonprofit Org.” service inscription, and again in May 1989 with a “Nonprofit 5-Digit ZIP+4” service inscription. The production/variety identifiers for these two versions are “(si-npo)” and “(si-zip),” respectively. This results in the following PNC Catalog Numbers for the service-inscribed versions of these issues:

• S21.1(si)-111111

• S21.1(si)-111121

• T5.5(si)-1

• T7.1(si-npo)-1

• T7.1(si-zip)-1

• T11C(si)-2

• T17.5(si)-1

A production/variety identifier is also necessary in PNC Catalog Numbers for the 29¢ Flower coil stamps and the non-denominated (32¢) G coil stamps produced by Stamp Venturers in 1991. Each of these stamps was produced with two different types of stamp separators. Some 100-stamp coils were processed with slit (or rouletted) perforations and the balance of the production was processed into coils with typical, round hole perforations.

The production/variety identifiers for these issues consist of a 4-letter abbreviation for the stamp separator types. For the PNCs with typical, round hole perforations, “perf” is enclosed in parentheses and included in the PNC Catalog Number after the design identifier component. PNC Catalog Numbers for PNCs with slit hole perforations include a production/variety identifier consisting of “slit” enclosed in parentheses.

The following list shows PNC Catalog Numbers for the 29¢ Flower and non-denominated (32¢) G coil stamps produced by Stamp Venturers:

• R29F(perf)-S1111

• R29F(perf)-S2222

• R29F(slit)-S1111

• C32G(perf)-S1111

• C32G(slit)-S1111

• C32G(perf)-S2222

Stamps that were only produced with round-hole perforations do not require a “perf” production/variety identifier.

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Adhesive Type Identifier

The PNC Catalog Numbering System associates each coil stamp with one of the following four primary adhesive types:

• Water Activated Gum (WAG) — stamps with any form of water-activated adhesive (such as dextrin or PVA)

• Pressure Sensitive Adhesive (PSA) — self-adhesive stamps that do not require moisture to activate the adhesive, are issued adjoined to one another on a continuous backing paper (liner) in a single vertical or horizontal row, and are divided by a shared die cut

• Pressure Sensitive Adhesive with Spaces — self-adhesive stamps that do not require moisture to activate the adhesive and are issued on a continuous backing paper with spaces between the individual stamps

• Linerless Self Adhesive — self-adhesive stamps that do not require moisture to activate the adhesive and are issued with the stamps wound in a roll that has the stamps adjoined to one another in a single vertical or horizontal row without backing paper (liner)

If a stamp design was produced in more than one of these primary adhesive types, the PNC Catalog Number for each version of the stamp design includes a distinctive adhesive type identifier. The Identifier for each adhesive type is a lower-case, 3-letter designation—except for the identifier for Pressure Sensitive Adhesive with Spaces, which encloses the three letters between a pair of squared brackets ( [ ] ).

The following designations are the adhesive type identifiers used in PNC Catalog Numbers:

• wag — for stamps with Water Activated Gum

• psa — for stamps with Pressure Sensitive Adhesive

• [psa] — for stamps with Pressure Sensitive Adhesive with Spaces

• lsa — for Linerless Self Adhesive stamps

If required, an adhesive type identifier appears to the immediate left of the separator (hyphen) of a PNC Catalog Number—after the series or set, denomination, design, and production/variety identifiers. The following examples illustrate the use of adhesive type identifiers in PNC Catalog Numbers for four different coil issues of the 32¢ Flag over Porch design:

• F32wag-11111 — represents the 32¢ Flag over Porch coil stamp with water-activated gum produced by the BEP with cylinder combination 11111

• F32psa-11111 — represents the 32¢ Flag over Porch coil stamp with pressure sensitive adhesive produced by the BEP with cylinder combination 11111

• F32[psa]-11111 — represents the 32¢ Flag over Porch coil stamp with pressure sensitive adhesive with spaces produced by the BEP with cylinder combination 11111

• F32lsa-M11111 — represents the linerless self-adhesive 32¢ Flag over Porch coil stamp produced by the 3M with cylinder combination M11111

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Separator

Each PNC Catalog Number includes a hyphen ( - ) that separates the more general information about the stamp issue (the series or set, denomination, production/variety, and adhesive type identifiers, when applicable) from the plate-number-specific information. Therefore, by convention, the more general information about the stamp issue appears to the left of the separator (hyphen), and the plate number (and the tagging type identifier or the precancel type identifier, if applicable) appears on the right side.

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Plate Number

Every PNC Catalog Number identifies a specific plate number for the stamp it represents. The plate number (sleeve number or cylinder combination) is the first component to the right of the separator (hyphen) in the PNC Catalog Number. The plate number component replicates all of the digits as they appear on the stamp. It also includes all plate number prefixes such as A or S, which indicate that a vendor other than the BEP produced the stamp. For example, the BEP's intaglio-printed version of the 29¢ Flag over Mount Rushmore stamp from sleeve 1 is listed as F29MR-1, and ABN's gravure-printed version from the first cylinder combination is listed as F29MR-A11111.

Some plate numbers on stamps produced by the BEP include capitalized letters—such as A or B—at the right side of the printed plate number. These letters are part of the actual plate number. The BEP used them to show that the single digits (one for each color/printing cylinder) of a multi-digit cylinder combination had exceeded 9. The BEP employed this methodology to avoid using two-digit numbers for a single color in the multi-color cylinder combination. For example, the printed cylinder combination 9999 (which collectively represents the ninth yellow cylinder, the ninth red cylinder, the ninth dark blue cylinder, and the ninth light blue cylinder) for the 33¢ Flag over City coil stamp was followed by 1111A, 2222A, and then 3333A. This incremental pattern continued until 9999A, which was followed by 1111B and 2222B, respectively.

Please note that a “P” at the right side of a plate number in a PNC Catalog Number has a different function. It is a component of the PNC Catalog Number—not the printed plate number. The capitalized P indicates that the stamp was precanceled. See the description for precancel type identifiers later in this section.

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Tagging Type Identifier

Some PNC Catalog Numbers include a tagging type identifier to differentiate stamps that have similar designs but have different types of tagging. If applicable, a tagging type identifier appears to the right of the plate number component of a PNC Catalog Number for a stamp. A tagging type identifier consists of 2 or 3 lower-case letters that relate to the philatelic terms used for the primary tagging types found on PNCs.

The following tagging type identifiers are used in The Plate Number Coil Catalog:

• bt (block tagging) — indicates that the stamp has phosphorescent tagging that was applied in the shape of a rectangle (or block) over the printed image. PNCs that were only produced with block tagging do not require the bt tagging type identifier in their PNC Catalog Numbers.
  
  Some coil issues were produced with more than one size of tagging block. However, for any block tagged coil issue, the size of the tagging block is consistent throughout individual rolls of stamps. Variations in the size of the tagging blocks on an issue are indicative of changes in the printing process during the overall production of the issue.
  
  For example, the 20¢ Flag over the Supreme Court coil stamps exist with wide (approximately 18.2mm x 21.1mm) and narrow (approximately 15.6mm x 20.6mm) tagging blocks. These varieties exist because—like other issues that have more than one size of block tagging—production of the 20¢ Flag coil stamp was spread across more than one printing press.
  
  Although tagging block varieties are documented in The Plate Number Coil Catalog, PNC Catalog Numbers do not include specific designations for these varieties. However, because the tagging block varieties correlate to the printing press or surfaces (plates, sleeves, or cylinders) used to print the stamps (which are represented in the primary components of the PNC Catalog Numbering System), the tagging block varieties are indirectly segregated by distinctive PNC Catalog Numbers.
  
  Returning to the example of the 20¢ Flag coil stamps as a demonstration of this indirect segregation, the following PNCs (represented by their PNC Catalog Numbers) have wide (or large) block tagging:
  
     · F20-1
     · F20-2
     · F20-3
     · F20-5
     · F20-11
     · F20-13
     · F20-14
  
  And, the other PNCs of this issue, which used different printing sleeves on a different press, have narrow (or small) block tagging:
  
     · F20-4
     · F20-6
     · F20-8
     · F20-9
     · F20-10
     · F20-12
   

• ot (overall tagging) — indicates that the stamp has phosphorescent tagging that was applied after the stamp’s image was printed. Overall tagging is intended to cover the entire surface area of all of the stamps in a production run; however, because of voids in the application roller or improper alignment of the application roller, some overall tagged stamps display untagged areas. Some stamps that were intended to have overall tagging exist without any trace of phosphorescent taggant. These completely untagged stamps are considered production errors, which are major varieties of the normal tagged stamp.
  
  PNCs that were only issued with overall tagging do not require the ot tagging type identifier in their PNC Catalog Numbers.

• ep (embedded phosphor) — indicates that the stamp has embedded phosphor tagging. This type of tagging integrates the phosphorescent taggant in the paper manufacturing process so that the tagging is dispersed into the paper web. When exposed to short-wave ultraviolet light, embedded phosphor paper looks mottled because the taggant penetrates the paper in irregular densities. Stamps produced with embedded phosphor paper exhibit a mottle UV reaction across the entire printed side of the stamp. Because the taggant is present in the paper prior to printing, the ink of the stamp’s design lies on top of the reactive taggant and, therefore, blocks the glow of the tagging in the printed areas.
  
  PNCs that were only produced on embedded phosphor paper do not require the ep tagging type identifier in their PNC Catalog Numbers.

• sp (surface phosphor) — indicates that the stamp has surface phosphor tagging. This type of tagging has phosphorescent taggant applied to the entire printable side of the paper web during the paper manufacturing process. Surface phosphor paper has an even (sometimes referred to as solid) appearance when exposed to short-wave ultraviolet light. Stamps printed on surface phosphor paper do not show any untagged areas. However, because the taggant is present across the surface of the paper prior to printing, the ink of the stamp’s design blocks the glow of the tagging in the printed areas.
  
  PNCs that were only produced on surface phosphor paper do not require the sp tagging type identifier in their PNC Catalog Numbers.
  
  Small quantities of the intaglio-printed 29¢ Flag over Mount Rushmore coil stamp (from sleeves 2 and 6) were printed on surface phosphor paper. This was the first use of surface phosphor paper in the production of a generally issued coil stamp. (In 1987, the USPS produced an experimental coil stamp using the design of the 22¢ Flag over the Capitol coil on phosphored paper to test the paper’s effectiveness to retain cancels on used stamps.) The surface phosphor variety of the 29¢ Flag over Mount Rushmore issue is commonly referred to as the “Lenz Paper” variety because it was originally reported by collector Joann Lenz.

• unt (untagged) —indicates that the nonprecanceled stamp was intentionally produced without phosphorescent tagging. This identifier should only be used in PNC Catalog Numbers for nonprecanceled PNCs that also exist in a tagged form. Therefore, nonprecanceled PNCs that were only produced without phosphorescent tagging do not require the unt Tagging Type Identifier. Additionally, this identifier should not be used in PNC Catalog Numbers to note untagged errors.

The 10¢ Canal Boat of the Transportation Series provides an exceptional example of tagging varieties within a single issue. Because this issue was intermittently printed over several years with only 5 different plate numbers, several of the plate numbers exist with more than one tagging variety—and collectively, the PNCs of this issue span the breadth of the tagging varieties described throughout The Plate Number Coil Catalog. The complete set of PNC Catalog Numbers listed below for the 10¢ Canal Boat shows how the Tagging Type Identifiers are used to describe each of the varieties.

• T10CB-1bt

• T10CB-1ot

• T10CB-1ep

• T10CB-2 (All examples of this PNC have embedded phosphor tagging.)

• T10CB-3 (All examples of this PNC have embedded phosphor tagging.)

• T10CB-4ep

• T10CB-4ot

• T10CB-5 (All examples of this PNC have surface phosphor tagging.)

The 10¢ Canal Boat also exists as an untagged error from sleeve 4. However, it is a production error and, therefore, is not included in the above list of PNC Catalog Numbers.

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Precancel Identifier

The PNC Catalog Numbering System denotes overprinted, precanceled PNCs with a precancel identifier—a capitalized “P” that appears in the PNC Catalog Number after the plate number component.

The following list of PNC Catalog Numbers for the 3.4¢ School Bus demonstrates how the precancel identifier is used to differentiate PNC Catalog Numbers of tagged PNCs from those of precanceled PNCs of the same issue:

• T3.4-1 — not precanceled

• T3.4-1P — precanceled

• T3.4-2 — not precanceled

• T3.4-2P — precanceled

All overprinted, precanceled PNCs are part of the Transportation Series. These overprinted precancels were applied over the printed stamps using flexographic or hard rubber mats on a specially adapted letterpress station on the printing press—except for the 11¢ Caboose, which used a routed-out tagging roller to apply two continuous, horizontal defacement lines (or bars). (Unlike precanceling on other Transportation Series stamps, the method of precanceling used on the 11¢ Caboose issue did not produce gaps in the horizontal bars.)
A precancel identifier is also used in the PNC Catalog Numbers for the precanceled versions of the following stamps:

• 20¢ Flag over the Supreme Court

• 18¢ Washington Monument

Of the two issues listed above, the 20¢ Flag over the Supreme Court had its precancel applied using the same process previously described for the 11¢ Caboose. The precancels of this issue were only produced on stamps printed from sleeve 14.

• F20-14 — not precanceled

• F20-14P — precanceled

In contrast, the text forming the precancel of the 18¢ Washington Monument stamp was printed using an additional black gravure printing cylinder during the normal printing process of the stamp. A separate gravure cylinder was used to print the black tone of the multi-color image. Applying the precancel in this way resulted in an additional digit appearing in the cylinder combination (plate number) for the precanceled PNCs of this issue in comparison to the cylinder combination of the tagged PNCs. Even though the PNC Catalog Numbers for the precanceled version of this issue can be differentiated by the additional digit in the plate number component, the precancel identifier is still included in its PNC Catalog Numbers for clarity. This is illustrated in the following list, which includes all of the PNC Catalog Numbers for the 18¢ Washington Monument issue:

• S18-1112 — not precanceled

• S18-11121P — precanceled

• S18-3333 — not precanceled

• S18-33333P — precanceled

• S18-43444P — precanceled

Most overprinted precancels exhibit anomalies from worn precanceling mats or variations in inking. Some of these anomalies—such as the missing period variety on the “Nonprofit Org.” overprint of the 3.4¢ School Bus—are consistent and are considered collectible by some specialists. However, the overprints of the 17¢ Electric Auto (originally issued in 1981) and the 10.1¢ Oil Wagon (originally issued in 1985) exist with significantly different overprint styles, which are considered major collectible varieties.

The 17¢ Electric Auto coil stamp has three distinct styles of overprints. Although each of these overprint style consist of a “PRESORTED FIRST-CLASS” service designation between two horizontal bars, the font differs in each overprint. By convention, the three styles of the 17¢ Electric Auto overprints are referred to as “A,” “B,” and “C.” The three styles are most easily identified by the length of the word “PRESORTED” in the top line of the service designation. The names of the styles equate to the overprints in the following manner:

• Style A — “PRESORTED” measures 11mm long

• Style B — “PRESORTED” measures 12.5mm long

• Style C — “PRESORTED” measures 13.5mm long

The three styles were produced from different sets of precanceling mats. Each set had four 108-subject mats (9 rows of 12 subjects) that were arranged two over two around the precanceling roller (which yielded a 432-subject mat). When mounted on the roller and engaged during press operation, the four mats needed two revolutions to overprint the 864 stamp impressions produced from a single revolution of the paired printing plates on the impression cylinder of the BEP’s Cottrell press.

Although the sets were produced as distinctive sets, mats showing style A and style B were mixed together in some of the production of the precanceled 17¢ Electric Auto coils. This resulted in se-tenant pairings of different precancel styles (A and B or B and A) at the meeting of the vertical edges of the precanceling mats, which is identified by the gap in the horizontal bars of the printed precancel.

The PNC Catalog Numbering System denotes each of the 17¢ Electric Auto precancel styles with a suffix consisting of a single lower-case letter, which follows the “P” in the associated PNC Catalog Numbers—“a” represents Style A, “b” represents Style B, and “c” represents Style C. When a 17¢ Electric Auto strip shows se-tenant examples of two of the precancel styles at the precancel gap, the PNC Catalog Number indicates the style as “ab” or “ba” to note the order of appearance from left to right. Each precancel identifier suffix relates to the precancel style name as follows:

• Pa — Precancel identifier used to denote a precanceled PNC strip of one or more stamps that only shows precancel Style A

• Pb — Precancel identifier used to denote a precanceled PNC strip of one or more stamps that only shows precancel Style B

• Pc — Precancel identifier used to denote a precanceled PNC strip of one or more stamps that only shows precancel Style C

• Pab — Precancel identifier used to denote a precanceled PNC strip of more than one stamp that shows precancel Style A on the left side of the precancel gap and Style B on the right side of the precancel gap

• Pba — Precancel identifier used to denote a precanceled PNC strip of more than one stamp that shows precancel Style B on the left side of the precancel gap and Style A on the right side of the precancel gap

Precancel mats from the third set (Style C) were never combined with mats from the first (Style A) or second (Style B) sets.

The following list shows all of the PNC Catalog Numbers of the precanceled 17¢ Electric Auto PNCs from plate 3 to illustrate the use of the precancel identifier with the suffix for the styles:

• T17EA-3Pa

• T17EA-3Pb

• T17EA-3Pab

• T17EA-3Pba

• T17EA-3Pc

A more obvious distinction exists on the overprints of the 10.1¢ Oil Wagon. When it was originally issued in 1985, the precanceled version of the 10.1¢ Oil Wagon was produced with a black overprint that consists of a “Bulk Rate” service designation between two horizontal defacement lines (or bars). In 1988, the 10.1¢ Oil Wagon was issued with red overprint consisting of a two-line, “Bulk Rate / Carrier Route Sort” service designation—without horizontal bars.

All precanceled 10.1¢ Oil Wagon stamps printed from sleeve 1 have the black overprint. Stamps printed from sleeve 2 have either the black or red overprint. All 10.1¢ Oil Wagon stamps printed with sleeve 3—the last sleeve used to print this issue— only exist with the red overprint.

To differentiate the different overprints of the 10.1¢ Oil Wagon stamps printed from sleeve 2, a suffix is added to the “P” of the precancel identifier. Each suffix consists of three lower-case letters—“blk” for the black overprint, and “red” for the red overprint. This results in the following PNC Catalog Numbers for the precanceled version of 10.1¢ Oil Wagon PNCs:

• T10.1-1P

• T10.1-2Pblk

• T10.1-2Pred

• T10.1-3P

The “Pblk” and “Pred” suffixes are not required for PNCs of precanceled stamps that were exclusively printed with black or red overprints.

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Part 2 — Extending PNC Catalog Numbers