Maybe, even then it is a bit of a stretch…

…how many (lost) Lancasters with 50cal Rose tail-turrets…..plus 1941 dated 303 ammunition?

I realise that it is perfectly possible for an aircraft shot-down in 1944 /1945 to be carrying 1941 (or earlier) ammunition but how likely is it? Maybe not so unlikely; Bomber Command aircraft probably didn’t fire much of the ammunition that they carried!

Quite possible for 1941 dated ammo to be carried on a late war aircraft. I own a couple of .303 Lee Enfield service rifles. A good few years ago now, around 2003, I acquired some surplus Mk7 ball ammo of mixed dates. Quite a few of those were dated 1941/42. So clearly they survived the war without being used. They still went bang!