Can Basement be considered part of gross living space

[Rick Turman]

I am currently under contract to sell a SFR flip here in Ohio and the buyer is questioning the square footage. We purchased the home base off MLS listing and our previous Auditor site posted as 3600 sqft 5 bd 4.5 ba which compares to the listing. The county switched companies December 2021 and now have a new Auditor site which now shows 2500 sqft 4bd 4.5 bath.

Buyer paid for an appraiser to calculate sqft today and the contract is contingent on this due to the deacrepency.

We have a full basement downstairs with kitchen and the bedroom has a massive egress slider window with stairs to climb out. Can the basement be calculated into this gross living since the egress window Is there? We believe it was calculated initially so we'd like to understand how to get it added.

Aside from this, how do you go about getting the County Auditor to correct the survey done whichever way this goes?

What can we do so this deal still will still be in our favor? Thanks all and looking forward to everyone's feedback!