I thought it was one of the most basic rules of social conduct. You do not speak of a party/event unless you know for a fact that everyone you are taking to is attending said event. That's why you don't let children give out birthday party invitations at school, since they are probably not giving invites to everyone. This is the second time this has happened with the same group of people in a relatively short time frame, and it's getting annoying. Did none of their parents ever bother to teach them this rule, or do they just not abide by it? I do not know either way, but people, please sort out your behaviour!
Apparently after-grad has been planned already, and people are already putting down deposits to go. I thought the concept of after-grad was that the whole class goes and parties for one last night together. This perception was wrong, because I only just heard about the event. Maybe it's only for people who party regularly? In which case, I do not understand why so many underclassmen are able to attend.