31681.52. Every retirement allowance or optional death allowance, including an allowance payable to a survivor of a member, payable to or on account of any member of this system or of a superseded system who has been or was retired for service is hereby increased as follows:Period during whichPercentage of increase inretirement becamemonthly retirementeffectiveallowanceOn or prior to June 30, 1967 ........................ 10%12 months ended June 30, 1968 ........................ 8%12 months ended June 30, 1969 ........................ 6%12 months ended June 30, 1970 ........................ 4%12 months ended June 30, 1971 ........................ 2%In no event shall any allowance be increased by an amount greater than seventy-five dollars ($75) a month. A member with credit for 10 or more years of service in the system shall receive not less than twenty-five dollars ($25) a month.This section shall not be operative in any county until such time as the board of supervisors shall, by ordinance adopted by a majority vote, make the provisions of this section applicable in such county.(Added by Stats. 1973, Ch. 298.)