The gross assessed total tangible property valuation for ad valorem tax purposes in each county, or service-ability factor, shall be determined from the county assessor's certificate of such valuations as filed with the excise board of the county for the purpose of computation of ad valorem tax levies of each year, and no subsequent amendments thereto to effect an increase or decrease in such valuations shall have any effect for such year whatsoever.
Okla. Stat. tit. 19, § 180.59