When assessments in a taxing district are reduced subsequent to the date when the county board of taxation has determined the amount of money to be raised in the taxing district on account of a state tax at a fixed rate, so that, pursuant to that determination, an excess over the amount which would have been payable if the assessments had been reduced before that date, must be paid to the county treasurer from the taxing district, the county board shall ascertain the amount of such excess.
N.J.S. § 54:4-50