This is my site and I can assure you that an incredible amount of time (and too much money) was spent researching and cataloging this set.
There are two distinct printings. However, not every card is affected by a change. Among the two print runs can be found slight variance in some cards but the lightened backgrounds, airbrushed jerseys, airbrushed lens flares/stadium lights and other changes are always uniform. For example: Matt Williams comes in two different jersey colors, not 'many' different, which would be the case if the cards were just the product of excess color misprinting. I've found each version of nearly every variation-affected card at least 3 or 4 times over during the five years I worked on these master sets.
Also, fyi, my list is likely missing a few of the much more minor variants.
Owner and creator of JunkWaxGems, online source for unlisted error, variation and oddball info from the junk wax era.