Refunding bonds bearing the signatures of officers of the municipality in office on the date of the signing thereof shall be valid and binding obligations of the municipality for all purposes, notwithstanding that before the delivery of the bonds any or all of the persons whose signatures appear thereon shall have ceased to be officers of the municipality, the same as if such persons had continued to be officers of the municipality until after the delivery of the bonds. A resolution authorizing the issuance of refunding bonds may provide that any such bonds may contain a recital that such bonds are issued pursuant to this chapter, and any refunding bonds containing such recital under authority of any such resolution shall be deemed conclusively to be valid and to have been issued in conformity with the provisions of this chapter.