by this section shall apply to taxable years beginning after December 31, 2016. 5. Statutory construction This Act is remedial Indian legislation enacted under the plenary authority of the Congress under the Constitution of the United States to regulate Indian affairs, and any ambiguities in section 139F or 250 of the Internal Revenue Code of 1986, as added by this Act, shall be resolved in favor of Native Corporations attempting to exclude income or claim a deduction thereunder.