California Code, Revenue and Taxation Code - RTC § 1603.5

(a) In the event a duplicate application for reduction in assessment is filed with the county board, the clerk may accept only the first application for reduction filed by or on behalf of the taxpayer, and may reject any duplicate application for reduction.

(b) For purposes of this section, “duplicate application for reduction” means an application for reduction filed by an applicant, or by his or her agent or attorney on his or her behalf, subsequent to an application for reduction previously filed by or on behalf of the same applicant, that seeks the same relief with respect to the same property for the same year in issue. A subsequent application for reduction that seeks to amend a previously filed application for reduction shall not be considered a duplicate application for reduction for purposes of this section.