There's literally never any way to predict who exactly will come out of the stage door and when. They might be having an off-day, they might be tired, they might be sick, they might not want to spend 20 minutes signing and taking pictures. Even if there are general trends, it's impossible to predict. You just have to go with it, see who you see, appreciate the opportunity, and not hold anything against those who don't come out of the stage door.