Card Identification Forum

OK all you baseball card sleuths.  I need some help.  The 1997 Upper Deck set has 18 variations listed, all within the "Capture the Flag" subset.  Six of these variations have images of the back, which show a white background.  I was able to very easily obtain these six cards.  Twelve of the variations have no images of the back of the card, and I can find absolutely zero mention anywhere on the internet that those 12 variations actually exist.

Whenever I search for the white back variations, I come up with the six I already have.  I sent a message to the two collectors that claim to have these 12 variations, and neither of them replied.  I sent a message to a seller on eBay that had the Rusty Greer card listed, and he responded that he doesn't actually have the card, never did, and removed the listing.

I know it is hard to prove that something doesn't exist, but does anybody have any thoughts on this?  Should they be removed from the database?  I would think with how easy it is to find the other 6 that there would at least be some mention of these 12 somewhere, even if the prices were crazy high.