(a) Except as provided in subdivision (b), a retirement allowance, optional death allowance, or annual 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including an allowance payable to a survivor of a member, payable to or on account of any member of this system or of a superseded system who has been or was retired for disability which did not on July 1, 1976, exceed five hundred dollars ($500) per month is hereby increased as follows:
Number of years of
Percentage of increase
county or district
in monthly retirement
service
allowance
25 or more years
10%
20–25 years
8%
15–20 years
6%
(b) No allowance shall be increased to more than five hundred dollars ($500) per month pursuant to subdivision (a).
This section shall not be operative in a county until such time as the board of supervisors shall, by resolution adopted by majority vote, make the provisions of this section applicable in that county.