For all buildings with non-conforming uses utilizing any of the provisions of this Section, the amount of pre-existing non-conforming floor area and pre-existing non-compliances, as applicable, shall be based either on construction documents for such building that were previously approved by the Department of Buildings at the time of construction, enlargement, or subsequent alteration, as applicable, of the building or, where an approved set of construction documents does not exist for such building, an as-built drawing set completed by a professional engineer or architect. The Department of Buildings may request additional information to substantiate proof of non-conformances and non-compliances, as applicable. Verification by the Department of Buildings of such documentation shall be a pre-condition prior to any demolition for reconstruction work, or alteration permit issued by the Department of Buildings for a zoning lot altering or reconstructing buildings with non-conforming uses and non-compliances, as applicable, pursuant to the provisions of this Section.