If bonds or notes are advertised for public sale and no conforming bid is received or if all bids are returned unopened, then the local government unit may cancel the sale and devise a new series for sale or, in the alternative, it may sell the series parts from time to time during the ensuing six months at private sale in accordance with the terms originally advertised with any changes in call price or dates of call for prior redemption or both as may be deemed desirable. After the six-month period, the local government unit may sell any unsold portion of the series in any manner permitted by this subpart, with such appropriate changes in the call prices or dates or call for prior redemption or both or in other terms as may be deemed advisable, provided that, as so changed, the two portions of the series when combined and any issue of which the series is a part are in conformity with the requirements of this subpart as to term, interest rate and stated maturities.