Avery---not sure I am following all your points about the differences you are seeing and pointing out. Ted Z, myself and others have posted cream and gray back examples of certain cards side by side in the 52 Gallery thread and the differences are easier to see that way than with just one or the other in hand or in a scan. As Ted S points out most of the gray backs also have dull drab fronts that normally look much different from the cream fronts
I think with the printing process of that time you will often see shade difference in color on the fronts and backs. Some of the front differences have been highlighted in the Gallery thread.
Here are my cream backs of the two cards you posted
