I guess the Chicago show has taken away many viewers as well it should. Some of the clues that showed up here were German, secret, production code. Binder mentions byf for a Mauser luger and Trooper mentioned byf or a P.38. The two missing are ac for Walther and cyq for Spreewerk.
Sometime about mid to late 41 the army realized that Walther could not meet the prouction needs of the army for the P.38 so they enlisted Mauser, who were dragged kicking and screaming from producing the P.08 Luger, and Spreewerk to pick up the slack.
These letter groups were assigned to these companies as to others so that the army could follow production and still keep the factory locations secret from allied intelligence services. This appears to have worked somewhat for P.38 production as although Walther and Mauser factories were well known to the allies even before the war, Spreewerk located in Grottau, CZ was never bombed throughout the war and only stopped production when the Russians walked in. I realize that this trivia was a little deeper than other questions on this forum and I appreciate those who participated.
Cheers,
Bill W