This is the first tech order I have found detailing the marking however that doesn't mean there were not earlier dated ones issued.Dated September 1944? I'm thinking that German armorers had more pressing issues at the time.
I agree, its just an interesting thing. There is a similar order out there for anti-tank rifles. The Germans ordered them all recalled at a certain, presumably for scrapping, as the guns were pretty useless after 1941.This is the first tech order I have found detailing the marking however that doesn't mean there were not earlier dated ones issued.