I checked and the serial correspond to a Coyne-Towers signature. The Beattie-Coyne begins at serial #1440001, so the B/C showed cannot exist. It can even not be an error since a so low number means that the serie had just began and it was impossible to know at that moment who will be the next Deputy Governor/Governor combination, no mention to get any correctly engraved plates...
I agree with this. The signature dies for Beattie-Coyne did not exist when this note was printed. It is extremely unlikely that a sheet of notes was sitting around with serial numbers but no signatures, and then got mixed into the later series to have the B-C signatures added. A slightly more plausible explanation but still extremely unlikely (in my opinion only) is that the serial numbers are wrong, either set incorrectly by the machine operator or changed during a print run the way mismatched numbers occur. If that was the case, there would be more notes like this and I doubt it would have taken 60 years for another one to surface.
Some observations...
The eBay listing does not contain the word "error". The words used in the listing, "extra rare", could mean anything. There is no guarantee given by the seller that the buyer will receive the item shown.
The given grade is Unc, but the note has a fold on the bottom left corner (as seen on the back side). The corners of the note are also rounded and clean. The note does not demonstrate any evidence of original condition, and, at least to me, looks pressed.
The seller did a really nice job of overlaying the image of the front of the note on the image of the back. Similarly, if I wanted to create a note of this apparent error type, I would take two $50 notes, one Coyne-Towers and one Beattie-Coyne, scan them at the same resolution and optics, and copy and paste the first two digits of the serial number of the C-T note onto the image of the B-C note. In fact, I did this sort of thing years ago when I created a humorous page on the Internet containing several fake errors. Manipulating images of paper money is relatively easy.
Have a very close look at the zeroes (00) at the start of each serial number. There is a tiny black blip inside the first 0 on the left side and inside the second 0 on the right side. Everything about these two 0's looks exactly the same. Similarly, the second 0 on the left and the first 0 on the right also appear 100% identical to each other. To me, this is done by the process I described above, i.e., copying and pasting details from another note.
For anyone who can afford 1925 $500 notes, this is the find of a lifetime. Go for it. And I hope the buyer shares with us what he/she receives in the mail.
