Some info here - apparently the second P-61 was hit by friendly AAA fire but struggled back to Giebelstadt, another crashed on landing after a similar patrol on the same night:
http://forum.armyairforces.com/tm.as...mpage=1#180119
The one written off in the crash at Giebelstadt was 42-39420: see this page (which I think has been "lifted" from Joe Baugher's site...)
http://napoleon130.tripod.com/p61blackwidow/id23.html
Looks like the other aircraft (hit by AAA fire, returned on one engine, crew unhurt) must have gone back on ops / been disposed of at some other time.
Maybe try posting in the Army Air Forces Forum thread - "Brickeisel" has written a history of Beaufighters in US service, knows his way around the 417th NFS.