Yep, all those are real varieties. Both the cut lines and the stock. The same stock thing happens for 68 and 69 too.
And some cards have different cut lines for the same color. Like wide or narrow white line.
I believe the white backs are really on the same stiock, but have had a layer of white added for some reason. Maybe to brighten the backs? But it's odd they'd do it off and on for three years.
I've been slowly collecting them for a while. so I have four groups, centered white back, centered cream back, and both with lines or not. it makes sorting a new batch a nuisance.
Steve B