When there is insufficient data upon which to establish mortality rates or other actuarial assumptions required to evaluate the obligations of the system, the board may adopt appropriate assumptions which are necessary, upon the advice and recommendation of the actuary.

All computations, payments, and other acts previously made or done by the board or its officers and employees which would be valid if this section has been in effect at the time the computations, payments, or other acts were made or done are hereby ratified, confirmed, and validated.