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PCThe "Big League" banner at the bottom of the lighter/brighter versions of the Gehrig and Foxx cards have a magenta tint, whereas the darker versions are more red/orange. Not sure if that is uniformly the case. (Also, the magenta shows up on the letter on Foxx's uniform.)
I'm not familiar with the Goudey print runs, but I would guess that printing the same card with a different number was Goudey's way of double (or triple) printing certain cards. And with Ruth, Gehrig and Foxx being so popular, maybe Goudey printed more of them to increase the chances of getting one of them (on the theory that a happy customer is a repeat customer).
Of course, that does not explain why the Walberg card appears twice. However, the Walberg cards are in fact two DIFFERENT cards. The one on the left has a blue sky, the image appears more in the forground, and the shoes are black. The one on the right has no sky, the image is more toward the background, and the shoes are clearly brown (not a lighter shade of black). Two similar, but different, cards, whereas Gehrig and Foxx are, to my eye, identical except for slight color variations.