Normally when you find a card like this, without a number, in a different design, it was used as a promotional card. Score was infamous for doing this. These cards usually started out at a high price market and then as the set was realeased and time went by the card usually went to the cellar. The same picture was usually used in the set or they could have changed it and left the back the same. Either way, what you have is a card that is probrably unusual and unique, but far from rare or even collectible. If your a huge Steve Young fan you got something.
"Don't dig up the past, all ya get is dirty"