I agree. I'm not going to say there is a variation on every pose but there sure are a lot of them. There's a big difference between these variations and legitimate changes that were made to the plates (on purpose) resulting in a wholly different card. Many of the proofs show these changes that were made (i.e., Leon's Matty). You can see many differences (not so subtle) which are readily apparent. Partial G, partial S, and all these that happen during the course of printing are somewhat interesting but more of an insight into the printing process itself rather than the intentions of the printers or the company that made the cards.
I've found a couple over the course of collecting just by putting some of the same cards side by side. Here's one I found. I didn't ascribe any value to it but if others do, so be it.
http://www.net54baseball.com/showthread.php?t=135461