Be it further enacted, that the City Council shall estimate the probable life of improvements proposed to be erected or purchased with the proceeds of any such bonds and the term of such bonds shall not exceed such probable life, provided that such estimate, if erroneous, shall not affect the validity of such bonds. (As amended by Priv. Acts 1995, ch. 55, sec. 2 and Priv. Acts 2014, ch. 55, sec. 1)