California Code, Revenue and Taxation Code - RTC § 4876.5

When it can be ascertained by the board from an audit of an assessee's books of account or other papers that the property of the assessee was incorrectly valued or misclassified for any cause, then to the extent that this error caused the board to assess taxable tangible property which should not have been assessed or to assess it at a higher valuation than the board would have entered on the roll if the error had not occurred, the roll may be corrected under this article at any time within four years after the assessment was made or within the period for which a waiver is given pursuant to Section 868.