No obligations issued after July 1, 1917 for school purposes shall be renewed or refunded, except such as are authorized by law to be renewed or refunded and except temporary loan bonds issued or to be issued in anticipation of the sale of permanent bonds pursuant to this chapter or to Title 18 of the Revised Statutes but this section shall not invalidate any bonds heretofore renewed or refunded pursuant to law.

L.1967, c.271.