Annual levies under such amended or new contract for the purpose of making payments due the United States may be made by the board of directors either before or after judicial confirmation of such apportionment of benefits upon the basis of the gross annual acre income of the lands of the district or divisions thereof, or the classes of lands therein, as such gross average annual acre income is determined by the secretary of the interior, until the amount apportioned against each tract has been fully paid and such annual levies shall include an amount sufficient to meet estimated delinquencies and any deficiency in collections arising from delinquencies in the assessments of the previous year or years for such purpose: provided, that no annual levies in excess of the levies which would have been required under prior contracts and apportionments shall be made prior to judicial confirmation of such new apportionment.