When you get into small schools it gets really wild. I taught in a 2A HS where we started as 6th graders, had a 7th grade MS band, then marched 8th graders. Other 2As in our region started 5th graders and did not march 8th graders. Same C MS class. I was putting 2nd year 7th graders on after 3rd/4th year 7th/8th graders.
The more complicated you try to make it to make it 'fair' the more problems will crop up. I think this is where the KISS principle applies and just work with it.