Short version: turn off the part of your brain that knows the chronology of World War II and you will be fine.
Slightly longer version: Guy Ritchie made up a bunch of [expletive deleted] for THE LEAGUE OF UNGENTLEMANLY WARFARE, mostly involving high-pressure domestic/foreign stakes that simply did not exist at that particular moment in time. …Do not allow yourself to care. You are there to watch the good guys kill the bad guys in an entertaining and madcap fashion, up to and including shooting them with arrows. It’s a video game mission brought to the full screen, complete with absolutely impossible silencers and bodies that conveniently disappear before anyone discovers them, and that is fine. That’s what I was there to watch. It’s a fun movie.