No petition entertained, no investigation made, no election held, and no certification issued by the National Labor Relations Board, under any of the provisions of section 159 of this title, shall be invalid by reason of the failure of the Congress of Industrial Organizations to have complied with the requirements of section 159(f), (g), or (h) of this title prior to December 22, 1949, or by reason of the failure of the American Federation of Labor to have complied with the provisions of section 159(f), (g), or (h) of this title prior to November 7, 1947: Provided, That no liability shall be imposed under any provision of this chapter upon any person for failure to honor any election or certificate referred to above, prior to October 22, 1951: Provided, however, That this proviso shall not have the effect of setting aside or in any way affecting judgments or decrees heretofore entered under section 160(e) or (f) of this title and which have become final.