(b) Any further such alterations for any class in any year may not exceed five percent of the base proportions or adjusted proportions used for the immediately preceding tax levy, provided that in each year the sum of any such proportions for such special assessing unit or portion thereof, or town or county special district or zone of assessment included therein, shall equal one. Such alterations may vary among portions and among town and county special districts; provided, however, that for town and county special districts and zones of assessment, any such alterations shall not be inconsistent with any changes in the value of the class in the special district as indicated by the assessed value of the class in the special district and the most relevant class equalization rates certified by the commissioner pursuant to section twelve hundred twelve of this chapter. 3. Town and county special districts. For purposes of town and county special districts that are not portions, the base proportion shall be determined by using the final assessment roll filed in calendar year two thousand one. The base proportion of a zone of assessment established from the territory of a prior district, as such term is defined in paragraph (f) of subdivision one of section four of chapter six hundred eighty-five of the laws of two thousand three, shall be determined by using the base proportion of the prior district with such adjustments, if any as are required by paragraph a of subdivision two of this section.