Notwithstanding Section 20481, monthly allowances payable to persons retired under a local system of a contracting agency at the time of contract shall be adjusted in accordance with this article. However, with respect to those retired persons under a contract effective on or after April 1, 1973, the “base year” shall be the year in which the contract is effective. Allowances payable for service to a public agency whose contract is terminated on or after December 1, 1969, shall be adjusted in accordance with this article subject to reduction in accordance with

Section 20577. Allowances payable for service to a public agency whose contract was terminated prior to December 1, 1969, shall not be adjusted in accordance with this article.