Seven U.S. states have used serial month coding on license plates at some point or another. The story isn't complete with states alone, however: Month coding caught a surprising second wind of popularity in four of America's overseas territorial possessions, starting in the 1970s and continuing straight on through to the present day.

Why is this? Why would four territories, isolated from the mainland and from each other by hundreds or thousands of miles of water, all spontaneously decide to do the same thing? A simple reason undoubtedly boils down to logistics. No island territory is set up to produce plates or registration materials locally: All rely on contract manufacturers like Irwin-Hodson of Oregon that may or may not even be in the same hemisphere of the world. A "simple" feat of issuing month stickers would require months of advance planning and lead time to order...and given the limited resources that territorial governments have, it would be an expensive proposition to make. It would have been much cheaper and simpler to take an existing stock of plates, divide it into tenths by digit, and assign each digit's lot a different expiration month.

U.S. Virgin Islands

The Virgin Islands were the first U.S. territory to implement staggered registration; in 1977. Old 1975-77 plates were divvied up into months by the final serial digit and were gradually replaced by a new coded design from January to October 1978. This in itself wasn't unprecedented: West Virginia replaced its last annual plate in similarly gradual fashion, and many states let their implementation of a staggered registration system coincide with a baseplate change. The exact way the U.S. Virgin Islands did things, however, was a bit odd.

The territory used windshield stickers as their vehicle for baseplate revalidation, not plate stickers. Thus, they usually relied on the plate to tell the month, and the windshield to tell the year!

Another oddity: Perhaps because the new plates had been ordered before the decision to implement staggered registration had been finalized, they expired in 1979 yet were dated "78." The Virgin Islands then fell into a continuous off-by-one error by issuing "79" windshield stickers expiring in 1980, "80" stickers expiring in 1981, and so on for years upon years afterward! It wasn't until 1995 that the territory finally backed away from this confusing system and started using the year of expiration for identification only.

The coding system itself was prosaic. The final digit of the serial indicated the month, with 1 to 9 indicating January through September and 0 indicating October. It seems that as with Massachusetts, new registrants in November and December were given October plates as well...so the highest numbers of any Virgin Islands plates of the 1980s and 1990s are in the October ("0") month series.

Months weren't the only codes on the plates, though. Starting in 1939 and continuing through the present day, the first serial character on Virgin Islands license plates has been an area code indicating either St. Croix (C), St. John (J), or St. Thomas (T). The U.S.V.I. is thus tied with Kansas in their status as having implemented compound month and political subdivision coding...though their three islands certainly pale next to Kansas' 103 counties in complexity of administration!

The U.S. Virgin Islands began to mark windshield stickers with expiration months in 1980, leaving the serial month codes as redundant deadweight. In spite of this, the system was retained through three subsequent baseplate reissues and persisted until the year 2000, when the territory reissued yet again and switched to an "ABC-123" serial format with no month codes.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct
1978-2000	1	2	3	4	5	6	7	8	9	0

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Guam

The Pacific island of Guam adopted staggered registration and month coding in 1978, four years into the life of their 1974-83 baseplate. The last digit was rigged up as an ex post facto month code, with 1 to 9 for January to September and 0 for October. Motorists jumped from the annual "77" sticker to various months in 1978 and 1979, with an option to extend the transitional renewal period as far ahead as September 1980.

This month-assignment system was simple for Guam to implement...and new plates were approached in the same way. Rather than cope with the logistics of having ten parallel month series that had to be ordered and stocked separately, Guam elected to retain a single sequential series of plates and pro-rated different expirations to new registrants based off the final serial digit.

Guam's month-coding system carried forth to the 1983-87 oxcart base, and was most likely used on the 1987-93 map base as well. In 1993 plates were reissued, month stickers were given out, and serial digits no longer corresponded with expiration months.

One consequence of this island's implementation of staggered registration was that an incredible rarity was created. "78" stickers were distributed only briefly, only to motorists whose plates ended in "0" for expiration in October (and possibly "9" for September), and only to those who declined to extend their registration interval to 1979.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct
1978-93?	1	2	3	4	5	6	7	8	9	0

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American Samoa

As with the U.S. Virgin Islands, American Samoa let their switch to a staggered registration system coincide with a baseplate reissue. 1977-79 plates were replaced by green "1980" issues, stickered and expiring in 1981. The first digit was a month code, with 1 to 9 indicating January through September and 0 indicating October, as usual.

A curiosity of American Samoa's system was that the territory supplemented the month codes with month designations printed on the stickers themselves.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct
1981-	1	2	3	4	5	6	7	8	9	0

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Northern Mariana Islands

The Commonwealth of the Northern Mariana Islands is a relatively recent political phenomenon: The islands have existed as a U.S. territory only since 1978, and were part of a U.N. trusteeship before that.

The C.N.M.I.'s current baseplate dates back to at least 1989 (or over two-thirds of the Commonwealth's entire history as such), and was neither coded nor staggered for its first decade and a half of issuance. At the end of the 2005 registration year, however, motorists were assigned to staggered expiration months...and they latched onto a last-digit system much like Guam's or American Samoa's to do so.

Predictably enough, 1 to 9 were used to indicate January through September, and 0 was used for October. There was a catch, though: November and December were also used as expiration months, and 1 and 2 were recruited to do double-duty for these! It would seem that the C.N.M.I.'s isn't a strict one-for-one coding system as much as it is a mnemonic to assign new expiration months by: New registrations may be assigned any month from January to December at any time of year and a single sequential numbering series has been retained. Interestingly the islands' foray into month coding also coincided with a foray into flat computer-printed license plates, though the territory appears to have since reverted to superior embossed issues.

	Jan Nov	Feb Dec	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct
2006-	1	2	3	4	5	6	7	8	9	0

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