If you are talking about on the Tax digest, please know that is information for the outside gross square footage. In georgia we do not quote square footage, other then from a public source such as the bulder plans, or tax digest. There is GREAT discussion in should a closet or alcove that is not very usable be include or not.
But if you see a big difference in what is quoted and what you believe it to be for gross footage, you can call the tax digest BUT beware , your property tax may go up if you tell them its bigger.
IF you are talking about sq footage wrong on a listing, call your listing agent