The adequate education program allotments of the public school districts and the funds derived from the supplemental school district tax levies authorized by law shall be used exclusively for the support, maintenance and operation of the schools in the manner provided by law for the fiscal years for which such funds were appropriated, collected or otherwise made available, and no part of said funds or allotments shall be used in paying any expenses incurred during any preceding fiscal year. However, this shall not be construed to prohibit the payment of expenses incurred during the fiscal year after the close of such fiscal year from amounts remaining on hand at the end of such fiscal year, provided that such expenses were properly payable from such amounts. Moreover, this shall not be construed to prohibit the payment of the salaries of superintendents, principals and teachers and other school employees whose salaries are payable in twelve (12) monthly installments after the close of the fiscal year from amounts on hand for such purpose at the end of the fiscal year.