Normally, part perf and imperf usages later than early-to-mid-1864 set off alarm bells for possible shenanigans as they were virtually all used up by that point. The major exception are the Late Date West Coast imperfs and part perfs. I’ve written about those before. Genuine imperfs and part perfs can be found with California, Oregon, and Washington cancels as late as 1870.

The East Coast is a different matter entirely. By the mid-1860s, virtually all imperfs and part perfs were used up, so other than an errant stamp or two presumably lost in someone’s drawer, there would have no reason for late-date usages to exist… and you just don’t find them.

You’re snakebitten on 3 fronts:

1. Even if a stamp looks genuine, if the cancel doesn’t name the location, you cannot attribute its usage to a particular geographic area; many revenue stamps are simply manuscript canceled with initials and a date… no business or city.
2. If you find an example with a discernable location that is purported to be an imperf or part perf, and it has a late date, 999 times out of a 1000 it won’t be a real imperf or part perf. The impression/color will be wrong or the margins will be insufficient.
3. Even if the color and impression are correct for an imperf or part perf and the margins are large enough, unless the stamp is still on document or is part of a correct-orientation multiple, the late date will be a disqualifier to most collectors.

So when I saw the item below on eBay, I had to buy it. Not that it is necessarily worth any more than a normal usage to the vast majority of collectors, but it is something that is truly scarce.

It is a vertical pair (!) of Scott #R1b, the 1-cent Express part perf, with a perfectly positioned November 3, 1868 cancel from the Cochituate Water Board Office in Boston, Mass.

It shouldn’t exist… but it does, and I’m thankful it survived.

P.S. The bottom stamp appears to have something going on in the word “CENT” at right, possibly one of the foreign entries known on R1?