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HankronI beleive that the progression proofs he offers are legitimate and likely originate from the Topps Auction, I cannot assure you that, as he says, each progression proof is unique, but each is rare (rarer than a Ty Cobb with Ty Cobb tobacco back).
Most to all of the progression proofs in the Topps auction were sold in sets (perhaps 6-9 different color variations per card). Like the Star Co. basketball and baseball sets, they are ordinarilly sold as sets not singles. This is not to say that there's anything wrong with selling the proofs as single, just pointing out the custom.
For those who don't know what is a progression proof: They were test cards made before the final print run. Used to test colors and color alignment, each card in the set showed a unique color combination (yellow, blue, yellow/blue, etc).
Below is a Hostess card (center) surrounded byits progression proofs.

I have no idea what is an 'enamel proof' or what Hagar means by an enamel proof (Is its surface enamel?). I've only heard the term used concerning Hagar's cards, and assum its something he coined.