School extensions - Public forum - Planning Advisory Service (PAS)

My question relates to the recent changes to part 32 of the GPD and the increase permitted development allowance to school building to a cumulative allowance of 100sqm of floor area. The issue is how this cumulative allowance is worked out In my authority there are two sections of thought, one lot take the view that if planning permission has been granted for extensions to the school that this uses up some or all of the allowance as the extension was not the original building. .The other stance is that only other buildings that have been constructed under the pd allowance should be considered and the floor area of development granted planning permission should not be included I would be grateful for any views on this