United States #17 Interesting Cancel

I don't have a better suggestion, and, as you said, it is impossible to say without a complete cover.

So I did some looking, and I definitely agree that the 19+38 together (with neither marked out) is highly unusual. Probably more so than I initially gave it credit for.

Maybe the stamp did not originate on that piece. Does the red ink match on the stamp and piece?

To your other question - spqr knows more than I, however, I don't tend to see mail in this period rated differently in Britain, unless maybe its forwarded or remailed, and they find out then. Maybe that's just because its usually rated correctly in the US. Mail to France got corrected there all the time since they used a different scale.

I don't see anything tying the stamp(s) to the piece - maybe some stray black ink near the bottom of the stamps, but that's not definitive at all. The red ink on the two numbers appears to be the same shade. The piece came with a clear 1994 PFC, for whatever that's worth. The piece and the cert are in the bank, so they are not available to view right now, and I don't have a scan of the cert. Anyway, Siegel's is highly reputable and Saadi, too. If there were any post-1850's shenanigans going on with this, I have no doubt Siegel's and Saadi were unaware.

This may simply remain a mystery.

ETA: I looked up the cert on the PF site. It says:

"ON PIECE, RED NUMERAL "38" CANCEL, RED "19" ACCOUNTING HANDSTAMP AND "PAID IN AMERICA" TRANSIT MARKING. AND WE ARE OF THE OPINION THAT
It Is Genuinely Used On Piece"

It is almost as if they are treating the two numbers differently.

The mails were accompanied by letter bills (you can see an example in the published treaty - 8th page of this .pdf - https://d2jf3tgwe889fp.cloudfront.n...UKTreaty.pdf).
When the mail got to Liverpool, they would settle based on the letter bill rather than re-rating each cover. Since the marks are in red the letter was paid at least as far as Liverpool, so they didn't need to collect any US or sea postage from the recipient, so an extra marking shouldn't cause too much trouble - it just looked odd to me

Thanks for the explanation, SPQR. Thank you for the input, also, txstamp.

Tx: unfortunately not my cover. Just one I happened to see for sale and it had that on it, which was something I also wondered about. Beautiful cover though, whoever owns it!

I posted this to another thread, but it seems to belong here better.

The '3' credit is used instead of 19 here since this was carried on an American owned mail packet. As such the US retained the 16c packet fee. Only the British inland transit of 3c was credited to Britain here.