(1) If the boundaries of a school district will change in the ensuing year, the Superintendent of Public Instruction must be notified by April 25 of the year prior to the change. Upon notification of the change the Superintendent of Public Instruction will recalculate the district mill value per ANB and subsidy per mill for the ensuing year using the sum of the current year taxable valuations, the sum of the budgeted ANB, and the sum of the GTBA budget areas of the territories within the district(s) .