[DonVoigt]

There is no evidence it is anything but a 1939 commercial Mauser.
Not a rework, note the clean inside- it is a rust blued commercial luger, not a hot dipped EG rework. Though you cannot see it in the auction pictures, it is likely a "v" suffix pistol.

The proof is indeed a Crown U, used by Mauser in Oberndorf for commercial production, up to the 1939 promulgation of new markings. This 1939 is probably one of the "last" to have it. The Eagle/N was first used in January 1940.

For more complete info see "The Mauser Parabellum 1930-1946" by Hallock & van de Kamp.