Parents How do coaches decide groups for competition?

[Dream]

So we got our lists of groups and times for competition and some of the girls from our group are on one day and some another. It is not by age as we know when the birthdays are and it does not follow that. They are all competiting bronze but there is 2 groups one group on one day and the other the next day. I realize that not every club does it the same way but wonder how they might decide who to put where or if your gym even gets to make that decision or if the group putting on the events just tells them where they go. But if thst is the case what are some ways the host club would decide? Just curious and would ask my club but they have been very busy so no chance to talk to anyone who would know right at the moment!