"Retirement system coverage group," with respect to any retirement system, means all employees designated as a coverage group in Section 218(d)(4) of the Social Security Act for the purposes of Section 218(c) of the Social Security Act only. The services of employees in any retirement system coverage group that are included in an agreement shall then become for all purposes of the agreement services performed as members of the coverage group to which they otherwise belong.
Ca. Gov. Code § 22011