[rvcc]

So, I have this card from the 1994 SP line with Mo Vaughn on the front and Wade Boggs on the back but can't seem to find out anything about it. I have searched the internet, checked with Upper Deck and checked this site but nothing. I have other SP cards that are double sided. Can anyone tell me about these cards?

[zeprock]

They are misprints. I have several from the 1994 SP set too. Unfortunately they are considered flawed as it undoubtedly happened during the printing process and not the design process. There is very little value to them.

[rvcc]

They are misprints. I have several from the 1994 SP set too. Unfortunately they are considered flawed as it undoubtedly happened during the printing process and not the design process. There is very little value to them.

While they might be considered misprints, I am a set builder and would like to know if you have any idea how many there are.

[zeprock]

I do not know how many UD screwed up. I have the same card as you with Vaughn on front and Boggs on back. I also have Biggio with Roberto Alomar on the back, Maddux with Carl Everett on the back, Steinbach with McGwire on back, Chili Davis with Molitor on back, Matt Williams with Ozzie Smith on back and maybe a few others. They're just oddballs in my player collections. I wouldn't consider them part of the set. Misprints are mistakes. The same as getting a card that's missing the foil stamping on it or miscut so badly that two players are showing. They weren't "intended" to be part of the set.

[djohn]

This is a wrong-back style printing mistake. This happens when the printing sheet used for the back doesn't match the one used for the front. There are also blank front and blank back versions, where the sheet's front or back was printed but the other side was missed. During the 80s and 90s this could've happened to several sheets in succession before someone noticed (if they noticed at all). So it is typical that when you find one you will find others with the same mistake. However it is impossible to know how many of any particular printing mistake actually occurred in any given set.
That being said, there is no checklist for these types of mistakes, and they aren't considered part of the sets. Some player collectors or extreme set collectors will chase them down, but it's not typical.