If as a result of epidemics or other abnormal circumstances any county suffers an abnormal reduction in attendance during any year, the board of school finance, in order to assure an equitable allocation of aid, may in its computation for such aid, make adjustments in the average daily attendance figure.
The maximum limit to such adjustment shall be the average daily attendance used as a base in computing the allocation of aid for the previous year multiplied by the ratio that the net enrollment for the adjusted years bears to the net enrollment for the base year.