The provisions of this part extending rights to a member of this system or subjecting him or her to any limitation, by reason of his or her membership in a county retirement system shall also apply to members who terminated state employment and became an employee of a fire district within six months of the termination, and who were employees of the district at the time that the district became subject to the county retirement system.

This section shall only be operative with respect to a county where the board of supervisors has made Section 31840.5 applicable in that county.