(b) In the event that all claims to benefits payable to, or on behalf of, a retired member expire, and the accumulated contributions exceed the accumulated net benefit payments paid to or on behalf of the retired member, the balance in the retired member's account shall be paid to the person or persons as the retired member has nominated by written designation duly executed and filed with the board of trustees. If there is no designated person or persons surviving the retired member following the expiration of the claims, the excess of the accumulated contributions over the accumulated net benefit, if any, shall be paid to the retired member's estate: Provided, That the provisions of this section are retroactive to all members who entered retirement status on or after the ninth day of June, two thousand.