Except as otherwise provided in NRS 354.598747, if one or more local governments assume the functions previously performed by a local government that no longer exists, the Nevada Tax Commission shall add to the allowed revenue from taxes ad valorem otherwise allowable to the local government or local governments pursuant to NRS 354.59811 an amount equal to the allowed revenue from taxes ad valorem for the last fiscal year of existence of the local government whose functions were assumed. If more than one local government assumes the functions, the additional revenue must be divided among the local governments on the basis of the proportionate costs of the functions assumed. The Nevada Tax Commission shall not allow any increase in the allowed revenue from taxes ad valorem if the increase would result in a decrease in revenue of any local government in the county that does not assume those functions.