Cal. Elections Code § 2154

In the event that the county elections official receives an affidavit of registration, executed under penalty of perjury, that does not include portions of the information for which space is provided, the county elections official shall apply the following rebuttable presumptions: (a) If no middle name or initial is shown, it shall be presumed that none exists. (b) If no party preference is shown, it shall be presumed that the affiant has declined to disclose a party preference. The county elections official shall designate the affiant’s party preference as “Unknown” on a roster under Article 5 (commencing with Section 2183) and the affiant shall otherwise be treated as a “No Party Preference” voter. (c) If no execution date is shown, it shall be presumed that the affidavit was executed on or before the 15th day prior to the election, provided that (1) the affidavit is received by the county elections official on or before the 15th day before the election, or (2) the affidavit is postmarked on or before the 15th day before the election and received by mail by the county elections official. (d) If the affiant fails to identify his or her state of birth within the United States, it shall be presumed that the affiant was born in a state or territory of the United States if the birthplace of the affiant is shown as “United States,” “U.S.A.,” or other recognizable term designating the United States. The affiant’s failure to furnish his or her place of birth shall not preclude his or her affidavit of registration from being deemed complete.