Joop over at Jan Still's forum has given me some great background information on Mauser production of this period. See:
http://luger.gunboards.com/showthread.php?t=22017
There were apparently a small number of Military proofed Mauser Lugers made in mid 1942 from left over parts. Other military Lugers with Banner toggles have been observed.
The "g" date block would put this into May, 1942 production.
The "WR" mark is a generic production inspection mark meaning "Werks Revision" or "factory control".
Marc