Regarding the Rebuild series: does anyone know what's with the different DVD cover designs, please?

I don't even know which covers belong in which set (apart from the obvious plain covers with the titles of course).
Does each set have a specific name?
Is there any difference between content too?

"What's with them?" Not sure what you mean. Different releases (plain or limited edition); different countries; no variation you wouldn't expect, really. And yes, the design idea for a series can change before the first plan is worked out - nothing new there either: I subscribed to a new printed edition of Bach's organ music, and the first eight volumes all arrived in matching livery, but when the last two were released they'd changed the design - so now if I wanted to get a matching set I'd have to buy new copies of the first eight volumes again!