(a) On and after July 1, 1972, no pension provided under the closed plan which has been in effect for 3 years shall be subject to adjustment. This provision shall not apply to adjustments of pensions required to implement subsection (b) of this section.
(b) Effective September 1, 1972, the amount of any pension in effect on July 1, 1969, shall be the greater of:
(c) Any pension overpayments discovered as a result of audits made between May, 1971, and June 30, 1972, shall not be subject to recovery.