(a) A person shall not receive credit for the same service in two retirement systems supported wholly or in part by public funds under any circumstance.
(b) Nothing in this section shall preclude concurrent participation and credit for service in a public retirement system and in a deferred compensation plan established pursuant to Chapter 4 (commencing with Section 19993) or Chapter 8.6 (commencing with Section 19999.3) of Part 2.6 or pursuant to Article 1.1 (commencing with Section 53212) of Chapter 2 of Part 1 of Division 2 of Title 5, a tax-deferred retirement plan that meets the requirements of Section 40l(k) of Title 26 of the United States Code, or a money purchase pension plan and trust that meets the requirements of Section 401(a) of Title 26 of the United States Code.
(c) Nothing in this section shall preclude concurrent participation and credit for service in the defined benefit plan provided under this part and in a supplemental defined benefit plan maintained by the employer that meets the requirements of Section 401(a) of Title 26 of the United States Code, provided all of the following conditions exist:
(1) The defined benefit plan provided under this part has been designated as the employer’s primary plan for the person.
(2) The supplemental defined benefit plan has received a ruling from the Internal Revenue Service stating that the plan qualifies under Section 401(a) of Title 26 of the United States Code, and has furnished proof thereof to the employer and, upon request, to the board.
(3) The person’s participation in the supplemental defined benefit plan does not, in any way, interfere with the person’s rights to membership in the defined benefit plan, or any benefit provided, under this part.
(d) For purposes of this section only, a person who elects to purchase service as described in Section 21029.5 for his or her service with the California National Guard is deemed not to receive credit for the same service in two retirement systems supported wholly or in part by public funds.