I have no idea if they are faded cards or recurring print defects. In another thread there is a discussion of the 58 Aaron cards with the blue versus green background. The first couple that showed up went for high dollars on ebay since people thought they might be variants ( if a true variation involves an intentional change in a card, I do not think recurring print defects qualify).
But, then a bunch of the blue Aarons started to show up on ebay, probably manufactured by exposure to light. Of course there is a risk in exposing a higher dollar value card to light damage on the hope it will bring more money than the regular version
It might be worthwhile to take a less valuable but similar 70 rookie card and expose it to light and see how it compares to the Munson after such exposure.
The situation with the Aaron card, one of which I have, has led me to believe one would never know for sure if one had a true variant ( recurring print defect) or just a faded card in most cases