A few things -
Ben, have you actually been able to fade black? Typically black just won't fade since the pigment is Carbon. There are some black inks that are a chemical dye, but even that hardly ever fades.
The original card is most likely fading. The green on the 67 backs is actually green, not yellow and blue mixed. At the time, the color of the ink could be really variable as a special color was mixed by hand from a recepie. So maybe something like two parts blue one part yellow 1/2 part black 1/4 part white. The press operator would mix the inks, but the measuring wasn't precise, so the actual color could be darker, brighter, a bit more bluish or greenish.
What's there approximates the range of back colors, but the pattern is what I'd expect if the card had been under some fanned out cards.
Not at all uncommon, I had it happen to some cards I'd set on a window sill while sorting and forgot about. All cheap commons, so no big deal.
Probably could have made the lines wider but you'll get the idea.
The Westrum is pretty cool. A nice big flaw on the Magenta layer.
That sort of problem happens a couple ways. Keeping in mind that the plate is first wet, then inked, then applies the ink to the offset blanket which transfers the ink to the card. And that the ink is oily and pretty thick.
One way is if there's a bit of fluid on the plate. That can block or partly block the inking. But it usually shows a teardrop shape area, and this isn't quite right for that unless the affected area was huge and this is just the tail.
Another way is if something gets on the offset blanket. Sometimes the card or paper stock is flawed, and peels leaving a thin layer stuck to the blanket. (The blanket is a big rubber sheet) When it comes around again to get inked the paper bit gets inked too. But since it's not rubber it won't transfer the ink as well and you get an area with somewhat random partial inking. (In appearance, the pattern is actually related to the grain structure of the obstruction. Cloth would leave a cloth like pattern.)
I think the second one is what happened here.
Both are interesting cards, and illustrate different technical points. Fun stuff.
Steve B