If any officer whose signature, countersignature, or attestation appears on the bonds or coupons ceases to be such officer before the delivery of the bonds to the purchaser, the signature, countersignature, or attestation is valid and sufficient for all purposes as if he had remained in office until the delivery of the bonds. The signature on the coupons of the person who is auditor at the date of the bonds is valid although the bonds may be attested by a different person who is auditor at the time of their delivery.