No employer shall be subject to any liability or punishment under the Fair Labor Standards Act of 1938, as amended [ et seq.] (in any action or proceeding commenced prior to or on or after ), on account of the failure of said employer to pay an employee compensation for any period of overtime work performed prior to , if the compensation paid prior to , for such work was at least equal to the compensation which would have been payable for such work had section 7(d)(6) and (7) and section 7(g) of the Fair Labor Standards Act of 1938, as amended [, (7), (g)], been in effect at the time of such payment.29 U.S.C. 20129 U.S.C. 207(d)(6)January 24, 19501950-01-24July 20, 19491949-07-20July 20, 19491949-07-20