I heard rumors of a computer mistake one year when a particular sorority on my campus had a bunch of girls show up to Pref that they hadn't exactly expected, because they had cut these girls before that round. I'm not quite sure on the specifics or what eventually happened, but I guess they worked it out because nothing was ever said about it after rush was over. I have often wondered about how much of this goes on...with all the activity during rush week, I can understand how it would be hard to know if that girl everybody thought would "shine brighter in another house"
just sort of slipped through the cracks and got invited back or if there was some kind of computer glitch somewhere along the way.