Notwithstanding any other provisions of either part 4, 5 or 6 of this chapter, any person paying gross receipts privilege taxes under provisions of either part 4, 5 or 6 of this chapter, and who is entitled to credit against such taxes for franchise and excise taxes paid, shall be allowed such credit when final annual reports of both gross receipts taxes and franchise and excise taxes have been filed covering the corresponding tax base period; provided, that a taxpayer who has obtained an extension of time beyond August 1, within which to file the franchise and excise tax return for the taxpayer's most recently completed fiscal year ended prior to July 1, shall be allowed credit for all payments of franchise and excise taxes made for such corresponding tax base period.