Project close-out will occur when all costs to be paid with grant funds have been incurred, when the last progress report has been submitted and the last home is sold to a home buyer, and no later than six months after the date for completion set forth in the grant agreement with the respective grantee, or at such other time as the corporation may establish. At such time, the grantee must submit, in accordance with the corporation's requirements, documentation of its grant disbursements and records, a certification of completion and final cost. Any cash advanced in excess of the final cost must be refunded to the corporation.