I mostly DM, but I work up parties for fun, either randomizing composition by class or doing something like rolling stats in order. I don't keep track of how many concepts I have, and if I'm playing and I need to do something I haven't written up, I'll make something else up. It's no biggie. Most of the characters I write up, I write up as though they were in my campaign setting anyway, so there's at least a little revision going to be needed if I use one.