All petition papers comprising an initiative or referendum petition shall be assembled and filed with the City Clerk as one instrument. Within twenty days after a petition is filed, the City Clerk shall determine whether there is attached to each paper of the petition a proper statement of the circulator and whether the petition is signed by a sufficient number of qualified electors. The City Clerk shall declare any petition paper entirely invalid which does not have attached thereto an affidavit signed by the circulator thereof. If a petition paper is found to be signed by more persons than the number of signatures certified by the circulator, the last signatures in excess of the number certified shall be disregarded. If a petition paper is found to be signed by fewer persons than the number certified, the signatures shall be accepted unless void on other grounds. After completing his examination of the petition, the City Clerk shall certify the result thereof to Council at its next regular meeting. If he shall certify that the petition is insufficient he shall set forth in his certificate the particulars in which it is defective and shall at once notify the committee of the petitioners of his findings.