The retired pay of an eligible person who makes an election described in subsection (a) shall be recomputed, effective on the first day of the first month beginning after the person attains the eligible person’s retirement age, so as to be an amount equal to the amount of covered retired pay to which the eligible person would otherwise be entitled on that date if the annual increases, in the retired pay of the eligible person made to reflect changes in the Consumer Price Index, had been made in accordance with
section 1401a of this title.