; and none of the provisions of this subsection shall apply with respect to such benefit even though such benefit may have been so reduced prior to the onset of such disability. . 3. Effective date and redetermination of benefits The amendments made by this Act shall apply with respect to monthly insurance benefits payable under title II of the Social Security Act for months after the month in which this Act is enacted. The Commissioner of Social Security (without the necessity of any application therefor) shall redetermine the amount of any widow’s or widower’s insurance benefit which is payable for the month in which this Act is enacted in order to reflect such amendments as provided in the preceding sentence.