2004 Fleer Greats of the Game Baseball Forum

Received a card in a recent trade that that appears to be from this set. It is blue on front, but it has no serial number stamping /500 on the back. It is exactly similar to the images from card #'s 10, 34, 59 & 88 that are currently displayed. Would this be considered a misprint or would it have anything to do with the intellectual properties of Fleer in the process of being sold to Upper Deck?

https://www.tcdb.com/Trivia.cfm/sid/1713/2004-Fleer-Greats-of-the-Game

Could have been one the the ones set aside in case of a needed replacement that got out when they were liquidated.