BUMPING this older thread.
As promised in earlier replies, I would keep looking for a duplicate. I've never found one, but this recent one comes oh so close. I've been able to look a high quality scans, front and through scans, plus put it through retro-reveal. It is probably just a scrape, but posted again for your comments.
Scott 31, ACSC 110, the upright single watermark.



When I do a through scan, you can see that the watermark is clear of the error area, and we see that it is a marginal watermark.

The complicating factor is that we have a standard LATE Cancellation, but also a rough looking green area. Retroreveal wasn't conclusive, but certainly a bright white area:

What do you think ... just another one-off due to a paper scrape, or some variety that I can't find in my book? Thanks for looking.