I think that they're not picking based off of the birthday. I wandered around for hours and didn't see anyone with the "Is it your birthday?" shirts. I heard it was the Covergirl booth, but I don't think so. It's probably that Katy finds someone that she likes at one of her M&Gs- if not, they probably pick someone based on how they look, what they're wearing, etc. I would imagine it always has to do with connections.