They probably are making them for Varta, and when the order is complete they simply carry on running the machinery to use up whatever is left in the batching for the cell chemicals, and then simply flip over the casing sheet and print on the back of it to make the new casings. You probably will find a few Varta cells with the other branding inside the case ( I have seen this) where they were near the end, and put the last roll in with the double print instead of the inner print being a varnish only sealing coat. Remember the chemistry of the zinc carbon cell is very old, and thus all are pretty much the same blend, only the cheaper ones will have a lot more filler material ( often sawdust or chalk) added into the ble3nd to bulk it out and reduce the cost per cell, at the cost of capacity. Adding the filler to the remaining bulk is easy, as you do not have to stop the line but only add to the blender ahead of the pasting operations.