(a) On July 1, 1991, the monthly retirement benefit payable to retirants and beneficiaries of the State Police Retirement System who retired June 1, 1991, or before, shall be increased by four percent (4%) of the benefit payable on June 1, 1991.
(b) The increase in benefits provided in subsection (a) of this section shall be added to the monthly benefit after the annual postretirement increase based on the consumer price index has been applied, and the increase in subsection (a) of this section shall be added to the base annuity of the retirant or beneficiary.