(a) The board of trustees of each retirement system to which this chapter applies may adopt rules it finds necessary to implement the proportionate retirement program provided by this chapter.
(b) Each retirement system to which this chapter applies, under this chapter and other laws governing the particular system, is responsible for determining:
(1) the eligibility of its members for benefits, including whether sufficient combined service credit exists to qualify members for proportionate retirement benefits from that system; and
(2) the amount and duration of proportionate retirement benefits payable by that system.
(c) Each retirement system to which this chapter applies shall cooperate with the other retirement systems to which this chapter applies in the implementation of the proportionate retirement program.