(1) Beginning July 1, 2016, for officers who became members on or after July 1, 2016, if the annual valuation made by the actuary, as approved by the board, indicates that the retirement system is fully funded and has sufficient actuarial surplus to provide for a supplemental, lump-sum cost-of-living payment, the board may, in its discretion, elect to pay up to a maximum one and one-half percent supplemental, lump-sum cost-of-living payment to each retired member or beneficiary based on the retired member's or beneficiary's total monthly benefit through June 30 of the year for which the supplemental, lump-sum cost-of-living payment is being calculated. The supplemental, lump-sum cost-of-living payment shall be paid within sixty days after the board's decision. In no event shall the board declare a supplemental, lump-sum cost-of-living payment if such adjustment would cause the plan to be less than fully funded.

(2) For purposes of this section, fully funded means the unfunded actuarial accrued liability, based on the lesser of the actuarial value and the market value, under the entry age actuarial cost method, is less than zero on the most recent actuarial valuation date.

(3) Any decision or determination by the board to declare or not declare a cost-of-living payment or as to whether the annual valuation indicates a sufficient actuarial surplus to provide for a cost-of-living payment shall be made in the sole, absolute, and final discretion of the board and shall not be subject to challenge by any member or beneficiary. In no event shall the Legislature be constrained or limited in amending the system notwithstanding the effect of any such change upon the actuarial surplus of the system and the ability of the board to declare future cost-of-living payments.