Mis-printed bills, while rare, do make it into circulation. I had a $20 bill with a major “printed fold” error that I sold for $250. That particular bill had one corner folded after the back was printed, but before the front. As a result, one corner of the front of the bill was balnk and the reverse contained the ink from both prints. The error extended well into the portrait. From your description it does not sound like a printed fold, but more like a case of foreign material getting on the paper during the printing process. If the only error is a gap in the seal, then I doubt the bill would bring much of a premium, if any.
Error bills are only worth something to a collector, and collectors of “freak” currency are few and far between. In order to get the kind of exposure necessary to bring a lare premium, I had to list my bill, with photo, on a large on-line auction.
The overwhelming majority of people have more than the average (mean) number of legs. – E. Grebenik