Where the rate of duty in effect at any time is an intermediate stage under
section 2902(a) of this title, the proclamation made pursuant to subsection (a) may provide for the reduction of each rate of duty at each such stage proclaimed under such
section 2902(a) of this title by not more than 30 percent of such rate of duty, and may provide for a final rate of duty which is not less than 70 percent of the rate of duty proclaimed as the final stage under such
section 2902(a) of this title.