The determination of the rights of a retiree to benefits or rights of survivors or named beneficiaries to death or other benefits under this system shall be determined on the basis of the law governing the system which is in effect on the date of retirement of the retiree or death of the participant as the case may be and the right of any beneficiaries or contingent payees as herein provided shall be determined on the basis of the law governing this system which is in effect on the date of the death of the retiree or participant which gave rise to the rights of the beneficiary or contingent payee.