California Code, Probate Code - PROB § 8801

If the personal representative acquires knowledge of property to be administered in the decedent's estate that is not included in a prior inventory and appraisal, the personal representative shall file a supplemental inventory and appraisal of the property in the manner prescribed for an original inventory and appraisal. The supplemental inventory and appraisal shall be filed within four months after the personal representative acquires knowledge of the property. The court may allow such further time for filing a supplemental inventory and appraisal as is reasonable under the circumstances of the particular case.