Looks like just different levels of exposure during the printing process. There are some others that are similar, but I don't know that anyone collects them as such.
There are counterfeits of these sets, but normally they have a white or gray back, not the cream the originals were printed with. Counterfeit exhibits are also usually zoomed in from the original photo.
Here are six Del Ennis cards which show a difference in top/bottom border shading.
https://www.comc.com/Cards/Baseball/...d/COMC/G-VG-EX
I've only really seen value differences for the true variation cards, like different poses, teams, logo airbrushed out, etc.