as much as i can't stand oonyx, he is right about the reconnecting thing. the servers have 21 (43 for zm) slots, but at any one time there are only 20 (42 for zm) people playing. that's because the last slot is automatically kicked...at all times. so basically, when someone tries to join, they'll "join" and then be automatically kicked before they actually are "in". People are actually "in" once you see the line from steambans.com and the info about their steamID.
players in game watching chat will see "so-and-so has joined the game" and will see that each time the person tries to join.
so yes, oonyx is right that he probably was joining late. HOWEVEr, i find that it is common courtesy to announce to the ct's in game (once you join late and are in spec) that you joined late and intend to !zspawn. normally, they'll say there's no problem with it. but don't do it if there isn't much time left, or there are only a few cts left.
edit: this isn't even talking about the reserved slot. nobody w/ a reserved slot will ever fill that 21st (or 43rd) slot. it's only there to kick people from.