19 U.S. Code § 2013 - Effective date of proclamations
(a) Retroactive effect; authority of President
Subject to subsection (b) of this section, the President is authorized, notwithstanding section 1514 of this title or any other provision of law, to give retroactive effect to any proclamation issued pursuant to section 2011 of this title as of the earliest date after January 17, 1965, which he determines to be practicable.
(b) Filing of request with customs officer
In the case of liquidated customs entries, the retroactive effect pursuant to subsection (a) of this section of any proclamation shall apply only upon request therefor filed with the customs officer concerned on or before the 90th day after the date of such proclamation and subject to such other conditions as the President may specify.