I propose that characters who haven't "shown up" after a while are either "running late", "overslept", or they're simply late arrivals to the program, meaning the plane with them in it has yet to arrive.

That way, everyone doesn't have to have a introduction, we can have ours and then a plane with the rest of the new arrivals can show up and we'll be good for late posters without shitting on continuity....I like continuity...