Wow, so much to respond to! However, I felt it worth noting that if you look closely at those two sculpts, you can see that they are actually TOTALLY different sculpts, and that the mouth isn't some little molding accident. Look particularly at the waist.
However, I’ve literally just had a thought. Star Wars figures often have VERY minor differences. These differences are often the result of the figure being produced in a different country. An easy example is the Biker Scout. If the figure was made in Taiwan its head looks one way and if it was made in Mexico it looks another way. Here is a picture.
Okay, like I said, I believe that the MUSCLE sculpt variations stem from each family mold having two molds for each sculpt, giving us variation 1 and 2. Why is this significant? Arforbes has said that he has owned 50+ Satan Cross figures and has only ever seen 1 variation. I think this is significant and not a mere fluke. Hell, I picked up 15 copies of sculpt #060 and quickly found a variation that divided evenly between my 15 figures.
For whatever it's worth, I think this means Satan Cross was only on one side of the family mold/tree that he was on. I don't know what that means...
TGB said that since Kinkeshi and MUSCLE were mass produced that there were likely multiple copies of each family mold. That means that even if Satan Cross was only on the family mold once, there would still likely be multiple copies of the family mold. (However, TGB said he wouldn't 100% rule out there bing only one family mold, with two of each sculpt.)
I think it is very significant that SC only has one variation, and my hunch is it is directly related to him not being on the poster and only being found in flesh.
Here's a thought: Were the non-MUSCLE sculpt trees scrapped because they only had one copy of each sculpt on them, instead of two?