Cal. Gov. Code § 31678
Notwithstanding any other provision of this chapter, any member of a retirement association established in any county pursuant to this chapter, who upon retirement receives a retirement allowance calculated in accordance with Sections 31676.1, 31676.11, 31676.12, 31676.13, 31676.14, and 31676.15, shall have his or her retirement allowance calculated under each such section only for the period of time that the section was effective in the county.
The Legislature recognizes that counties subject to this chapter may adopt two or more of the enumerated retirement allowance calculation sections when changing from a section providing a lesser allowance to a section providing a larger allowance and thereby creates a windfall for a person who retires immediately after the adoption of a section providing the larger allowance because the retirement allowance is calculated as if the section had been in effect during the entire career of the member. The purpose of this section is to prevent this practice. This section shall apply only to persons who become members of the retirement system after January 1, 1981.
Ca. Gov. Code § 31678