I know that this isn't an evenly distribution, but it doesn't matter. If A has 20 trainees, B 15, C 5 and D 40, D can "give" for example 15 trainees to C and C will follow same method teached by D. This is only a way to give same position players to the same member of staff, so one member has only to think "how growing X position". This is a way to simplify the job, but not a strictly division.
Thank you :)