Occupancy values in ventilation calculations

Hello, one of our review comments was that the occupancy values we reported in the ventilation calculations were inconsistent with those reported in other credits. I am confused because the occupancy values used in the ventilation calculations were calculated by the mechanical engineer using occupant density listed on ASHRAE 62.1 and these are being compared to occupancy values (FTE) listed in PIF3 and other credits which are calculated by a different method. It seems logical to me that these values would vary slightly. Can someone tell me what I am missing? Thank you, Dan