Flipping through my '66 set I noticed something. Several of the semi-highs (447-522) in my album have different backs to them. Most of the backs are a more faded off-white/cream color. However, there are some (I'd say about 20%) with a distinctly different back color. These are much more bright white. There is also a very slightly different color scheme on the fronts as well - you can really tell a difference in the players faces
Another slight difference is in the paper stock. The bright white backs are a little bit "flimsier" and seem to be printed on a thinner card stock.
I don't see any listing anywhere of a back variation for this series. Was this a different print run? They all seem legit to me and I couldn't imagine '66 semi-high reprints to be that prevalent in the hobby where I'd have this many of them (and I got them all from reputable sources).
Curious if anyone has any insight on this. Do you notice these differences in your '66 set? Any knowledge about prior research on this variation?
I've uploaded some scans to my photobucket.
Front scans
Back scans