I'll be switched...
Only WorldCon I've ever been to was that one: MidAmeriCon, Kansas City, 1976. So we at least passed each other in the halls, or the art show, or somewhere like that.
First time I ever donated blood was there, to earn a way in to a special reception; RAH's life had been saved by transfusion, and it was allegedly his idea to have a blood drive at the Con. I've been a semi-regular donor ever since.
I still have my Progam Book, too - do you?