I have read about Luger "reworks" but admit that I am not sure exactly what that is, except a way of explaining something the "expert" using the term can't figure out. The date code on Luger receivers was heavily stamped and no "rework" is going to remove it without leaving a trace. The same goes for the code on the toggle.
So the only way a 42/42 could occur at the factory would be if a new (42) receiver were made up with a leftover or reject toggle with the old "42" Mauser code which had never been numbered. Possible? Maybe, but I would want to check such a gun VERY carefully. I would also wonder why no other mismatches turn up, like a byf toggle on a 1936 receiver or an S/42 toggle on a 1941 receiver.
FWIW, I have Datig, Kenyon, Görtz and Sturgess, and both Walter books and some Lugers, and still can't claim to know much about the Luger. I have had discussions with several self-proclaimed Luger experts, one of whom assured me that the Luger was a blowback pistol!!! I won't name him but he shows up on the Luger forums from time to time, still spouting nonsense.
Jim