I've been buying Topps art for card backs since 1991 and am by no means an expert.
The easiest to feel comfortable about? Those with the "Toppsvault" COA.
I have bought pieces from Mike Gidwitz (without the stamp or COA) whom I trust and since the price was very reasonable, it wouldn't bother me if they were found to be fake.
Another "group" of artwork that I would also have piece of mind? Those with the Auction (Guernsey) stamp on the back. Many dealers bought boatloads of these at the auction and were selling them in SCD in the early 90s.
What interests me about the artwork from the auction? It's not complete.
(No printing)
I can only guess that perhaps this was the part of the process where they were going to do a "paste-up" for a subsequent card proof?
I think these items are a bit overpriced now IMO. I'm totally out of the game for that kind of dough.