Nothing contained in this article shall affect in any way proceeding heretofore begun by the governing body of any political division to issue bonds under the authority of any statutes of this state heretofore in force. Such proceedings may be completed under the statute under which the same were begun and under the provisions of this article so far as the same can be made applicable thereto. Nor shall anything contained in this article invalidate any indebtedness heretofore incurred under a law then existing.