Sec. 25. EMPLOYEES ON RETIREMENT WHEN ACT TAKES EFFECT. (a) Any person receiving a retirement benefit from the predecessor system immediately before the effective date of this Act shall continue to receive the same benefit amount the person was entitled to receive under the predecessor system.

(b) This Act does not change the status of any former member receiving a pension, or who is eligible to receive a pension, from the city or the pension system under the predecessor system, unless otherwise expressly provided by this Act.