Revenue refunding bonds may be sold or exchanged in installments at different times or an entire issue or series may be sold or exchanged at one (1) time. Any issue or series of revenue refunding bonds may be exchanged in part or sold in part in installments at different times or at one (1) time. The revenue refunding bonds may be sold or exchanged at any time on, before, or after the maturity of any of the outstanding obligations to be refinanced by the revenue refunding bonds.