Rich
You are correct; a few 1940 42 code Lugers were originally issued with brown Krieghoff style grips. (Also a few were issued with black plastic grips, however this concept seems very controversial). In my opinion, a 1940 42 code is more valuable with correct brown grips.
Jan
See the links below:
BLACK GRIPS DATA REQUEST (Multi-page thread 1 2 3)taudelt
http://luger.gunboards.com/showthread.php?t=8859
1940/1941 DATES MILITARY CODES 42 and byf DATA (Multi-page thread 1 2 3 ... Last Page)Jan C Still
http://luger.gunboards.com/showthread.php?t=3695