"How could they have located and removed the luggage from five no-shows already in the hold, and still leave within six minutes of scheduled departure time? "
Especially on the late flights, they are typically closing the doors 10-15 minutes ahead of scheduled departure. Either they find and offload the bags OR the passengers turn up. Whichever comes first generally. And after the longhaul heavy traffic is already gone, taxi time is very short, so its entirely possible
But five is a large number and, whilst there may be nothing at all to it, is does warrant examination. And I'm sure they have done so. Just not given out any information.