WHOthe_DOCTOR

If the game is full, players who join the Waitlist are next in line for invites if there is a no-show. The waitlist # is the order they joined the waitlist and the order you should invite them in.

Reserve/ Backup players aren't expecting or waiting in line to play, but they wanted to let you know they're available if you need an extra. Make sure to invite all the waitlist players first.