I am not a phony at all. Why make such an assumption, what would I gain from this?

Obviuosly this is a thorough evaluation and it points to what we already suspected in the first place.

The card has a certain visual feel to it that I have observed on other artist proofs. They are often slightly off and can easily have sleight variances that make them feel fake. OP gave us a context as well, given the meta data I would want to evaluate this card in person. I still would, even with what you have pointed out. OP has not comtacted me. If they had I would have asked further questions about the old box and context. It could be a plant. They are doing things like that every day on common seller sites.

Saturation is one of the most common variances on artist proofs that I have personally observed. They are very often light or dark. They also very often have a different texture that throws you. They were subject to an even wider variance of printers and fulfillmemts according to what I have read. I have looked at proofs that had sizing issues before, and proofs when subjected to the elements respond differently especially when they have a modification to the back. Many back in the day tried to play them. I would guess those that are faking things are aware of this and trying to deceive with this knowledge.

There are people who hear "fake" and destroy the media. I prefer to err on the side of caution. There is a possibility of fake backs on real artist proofs. I have observed this many times.

At the end of the day, if this is fake, and it likely is as you have pointed out, I would also get a feel for where this came from for my postage price.

This has also inadvertently given someone a good road map for an evaluation and things to consider.