Subject to subsection (b) of this section, a disability retiree of the State Police Retirement System, or a beneficiary of a disability retiree of the State Police Retirement System, who retires on or before June 30, 1999, with an ordinary or special disability retirement allowance under § 29–107 or § 29–111 of this subtitle, shall receive an annual retirement allowance adjustment as of July 1, 1999, as follows: for a retiree who has been retired not more than 5 years, $1,200; for a retiree who has been retired more than 5 years but not more than 10 years, $1,500; for a retiree who has been retired more than 10 years but not more than 15 years, $1,800; and for a retiree who has been retired more than 15 years, $2,100. Each fiscal year, the Board of Trustees shall increase the adjustment received by the retiree or the beneficiary as of July 1, 1999, by multiplying the adjustment by a fraction that has: as its numerator, the Consumer Price Index for the calendar year ending December 31 of the preceding fiscal year; and as its denominator, the Consumer Price Index for the calendar year ending December 31, 1998.