Here is a puzzle that looks like a contradiction. A stamp is issued in two versions — perforated and imperforate. So how can there be an imperforate error of it? The imperforate one is not an error; it is a product.
The answer is a good demonstration of why plate numbers matter more than most collectors realise.
The stamp
A 2¢ carmine showing William H. Seward, issued 1 June 1909 to promote the Alaska-Yukon-Pacific Exposition, which opened in Seattle that same day.
Seward is the obvious choice of subject: as Secretary of State he negotiated the purchase of Alaska, the deal ridiculed at the time and vindicated by the exposition celebrating the territory forty-odd years later.
It was issued perforated (Scott 370) and imperforate (Scott 371).
The error
Scott lists 370a — described as an imperforate error, in a plate-number block of six carrying plate number 5209.
The explanation is in the plates. Panes that should have been perforated were found imperforate within perforated stock. That makes them an error of the perforated issue, not examples of the imperforate one.
And the only thing distinguishing them is the plate number, because plate 5209 was used exclusively to print the perforated version.
Which leads to an unusual collecting rule
Scott 370a can only be collected as a plate-number single or a multiple that includes the plate number.
Detach one of these stamps from its plate number and it becomes indistinguishable from an ordinary Scott 371 — same design, same absence of perforations, same everything. The evidence of what it is lives in the margin, not in the stamp.
The plate ranges make this concrete. The plates used for the issued imperforate stamps were also used for perforated printings, numbered between 5235 and 5357. Twelve plates were used for perforated stamps only, numbered 5142 through 5211 — and 5209 sits in that second group.
What it is worth, and the italics
Scott values 370a at $2,250 mint, and prints that figure in italics — the convention indicating an item that is difficult to value accurately, generally because too few change hands to establish a market.
It is not known used, which follows: anyone who noticed what they had did not mail it.
How many exist is not recorded. The catalogue note says "panes," plural, which implies at least two panes and two plate blocks per pane. Only one left-side plate number has been reported. The rest may be sitting unrecognised in collections, having been separated from their margins by somebody who did not know the margin was the whole point.
The lesson
Do not trim margins. Do not break up plate blocks. On a surprising number of items the identifying evidence is in the selvage, and once it is gone the stamp cannot be told apart from a common one — regardless of what it actually is.
This applies well below the rare-error level. Plate numbers, position markings and marginal inscriptions carry information, and removing them destroys value that the stamp itself does not show.
Best deals on Forever stamps
The opposite end of the market, and worth stating clearly. Modern Forever stamps have no plate-number premium worth chasing and no error market to speak of. Their value is postage, it rises with every rate increase, and you improve on it only by paying less than face at the outset.
Where to buy
Postage from USPS or below face from a verified surplus channel such as Forever Stamp Center — see the Forever range. For anything at the value discussed above, get an independent opinion before you buy.
The short version
Panes that should have been perforated turned up imperforate in perforated stock. Plate 5209 was only ever used for the perforated printing, so the plate number is the only proof — which is why Scott 370a can only be collected with its margin attached.
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USPS specialist based in Los Angeles with extensive experience in postal operations and customer service. Certified in mail management and trained at the USPS Business Mail Academy, she offers reliable guidance on Forever Stamps and practical mailing solutions.
