The highest annual average compensation during any consecutive 12- or 36-month period of employment as a member of a county retirement system shall be considered compensation earnable or pensionable compensation pursuant to Section 7522.34, whichever is applicable, by a member of this system for purposes of computing final compensation for the member provided:

person retiring after October 1, 1963, who entered membership prior to October 1, 1957, if the person entered the employment in which they became a member within 90 days of termination of employment in which they were a member of the other system, and they became a member within seven months of entry into employment, or, if an employee of a district as defined in Section 31468, became a member at the time the district was included in a county retirement system.