GOV §17615.5: (a) If any local agency or school district has an established base year entitlement which does not include costs for a particular mandate, that local agency or school district may submit reimbursement

(a) If any local agency or school district has an established base year entitlement which does not include costs for a particular mandate, that local agency or school district may submit reimbursement claims for a minimum of three consecutive years, adjusted pursuant to Section 17615.3 by changes in the deflator and workload, or entitlement claims covering a minimum of three consecutive years, after which time its base year entitlement may be adjusted by an amount necessary to fund the costs of that mandate. (b) If any local agency or school district has no base year entitlement, but wishes to begin claiming costs of one or more of the mandates included in the State Mandates Apportionment System, that local agency or school district may submit reimbursement claims for a minimum of three consecutive years, or entitlement claims covering the preceding three consecutive years, which shall be adjusted pursuant to Sections 17615.2 and 17615.3 by changes in the deflator and workload, after which time a base year entitlement may be established in an amount necessary to fund the costs of the mandate or mandates.