And what's to prevent anyone from simply booking their own trip and showing up at the convention?
Room 215 ...
Absolutely nothing. Face it, over 99% of the people attending an "International Convention" are just the people who would be going anyway, those whose congregations are assigned there.
Of course some are the locals who volunteer with the tours, entertainment, coordinate local activities, etc.
But it's just that 1% who actually are the ones "invited" as delegates (I guess they still call them delegates).
Rub a Dub