I was wondering what kind of plate errors are out there? I'm sure there are many. This one is very interesting; something I've never come across before on a sheet: http://www.ebay.com/itm/Uncut-4-Note-Sheet-1981-1-00-Richmond-E-E-Block-Back-Plate-ERROR-/290784005575 Is this definitely an error?
Yes. Plate# 7273 should be 3273. The plate numbers for the series didn't even reach 4000. There are others including "129" (plate number of the left side of the note instead of the right), "905" (should be 1905), and "295" (the number is a smaller font). I have examples: http://www.panix.com/~clay/currency/errors.html