County tax levy to be based on state assessment -- Exception for special taxing district

taxing district. The assessment made for state purposes, when supervised as required by law, shall be the basis for the levy of the ad valorem tax for county, school district, and all special taxing district purposes; except that any special taxing district established within an incorporated city under existing statutory or any independent school district whose January 1, 1975, assessment per pupil in average daily attendance would have been reduced because of the use of the assessment made for state purposes as of January 1, 1975, shall continue to use the assessment made for city purposes.