Thanks to a comment left on one of my posts I now know the origin of the Gary Sheffield mystery card!!
Fellow bloggers Swag of NYC Cards and Swag and The Chop Keeper of The Card Shop have said that it came from Score, Cherry Hill, NJ. I have done a few searches online and have found that this company was a leader of sports memorabilia and one of the players signed to them was indeed Gary Sheffield. I can not find the specific Sheffield card that I have but I'm 99.99% sure this is correct and I'm happy to close the books on this.
My apologies to the chop keeper, I obviously didn't read the full comment that he left and missed the part at the end where he said 'Cherry Hill'. Or maybe I didnt miss it and this was edited into the comment later. Anyway he was the first to name the company that it came from but Swag was the one that tied it all together. Swag may also have information on the Giants team ball which will tie up another mystery.
I mentioned that there was a prize for solving this and there is. I just need to find something for you both unless you want to share one prize and alternate it every six months!
I have two weeks off work now so this allows me the time to have a good look for something to send both these guys. So Swag and Chop Keeper expect an email from me at some point in the next week or two for your addresses and I can get something out to you. In the mean time if there any specific sets or collections that either of you are working on then please let me know.