Gov. Code, § 17615.2

(a) Notwithstanding Section 17561, after November 30, 1985, for those programs included in the State Mandates Apportionment System, after approval by the commission, there shall be disbursed by the Controller to each local agency and school district which has submitted a reimbursement claim for costs mandated by the state in the 1982–83, 1983–84, and the 1984–85 fiscal years, or any three consecutive fiscal years thereafter, an amount computed by averaging the approved reimbursement claims for this three-year period. The amount shall first be adjusted according to any changes in the deflator. The deflator shall be applied separately to each year’s costs for the three years which comprise the base period. Funds for these purposes shall be available to the extent they are provided for in the Budget Act of 1985 and the Budget Act for any subsequent fiscal year thereafter.

For purposes of this article, “base period” means the three fiscal years immediately succeeding the commission’s approval.

(b) When the Controller has made payment on claims prior to commission approval of the program for inclusion in the State Mandates Apportionment System, the payment shall be adjusted in the next apportionment to the amount which would have been subvened to the local agency or school district for that fiscal year had the State Mandates Apportionment System been in effect at the time of the initial payment.