California Code, Revenue and Taxation Code - RTC § 255.1

The assessor, whenever in his judgment good cause exists, may grant a reasonable extension of time for filing a claim for the homeowners' property tax exemption to any claimant who has filed a timely claim, but the claim is otherwise defective because it lacks either any of the required information or the signature of the claimant.

Only one extension shall be allowed to such claimant for any one filing period. No extension shall be more than six months from the due date provided for filing the claim, unless the assessor does not find and notify the claimant of the defect within a reasonable time to allow resubmission of the defective claim as corrected before the expiration of the six-month extension, in which case the assessor shall extend the permissible period for filing no more than three months from the time the defect or defects are found and the claimant is notified.