Here is a link to a great page with a lot of the '91 Topps errors and variations.
bnorth was also telling me something about some of the backs glowing under UV and some not, but I honestly can't remember at the moment if that was just factory sets or what.
I have sorted a TON of these, and I think I am only halfway there.
Sean
http://junkwaxgems.wordpress.com/201...list/#more-579