Revenue bonds or refunding bonds bearing the signatures of the appropriate officers who are in office on the date of signing are valid and binding obligations notwithstanding that before the delivery and payment any or all of the persons whose signatures appear on the bonds have ceased to be officers of the issuing district. The validity of the bonds is not dependent upon or affected by the validity or regularity of any proceedings relating to the acquisition, purchase, construction, reconstruction, improvement, betterment, or extension of the project for which the bonds are issued. The resolution authorizing the bonds may provide that the bonds must contain a recital that they are issued under this chapter and the recital is conclusive evidence of their validity and of the regularity of their issuance.