My guess is the developer reported gross building area which includes thickness of exterior wall areas and some interior open to below areas.
Someone took a look at the appraisal and saw it didn’t match because the appraiser is supposed to measure interior wall to wall floor space, excluding exterior walls and some stairwells. This can easily account for a 8-10% difference.
This is very common. I have, however, run into a couple projects where it appeared the developer also included patio or balcony space which is definatly misleading.
