(1) An eligible employee becomes a member of a retirement system on his first day of covered employment under that system.

(2) A member of PERS or sheriffs' retirement system who elects to requalify previously refunded service in his current system shall have, as his first day of membership, the first day of his requalified service.

(3) A member of the police or firefighters' unified retirement systems shall not have his first day of membership changed by any election to requalify previously refunded service.

(4) A member of a retirement system will not affect his first day of membership service because of any voluntary election to transfer service credits into this system from another system or to qualify any other full-time public service employment or military service.