California Code, Code of Civil Procedure - CCP § 2030.310

(a) Without leave of court, a party may serve an amended answer to any interrogatory that contains information subsequently discovered, inadvertently omitted, or mistakenly stated in the initial interrogatory. At the trial of the action, the propounding party or any other party may use the initial answer under Section 2030.410, and the responding party may then use the amended answer.

(b) The party who propounded an interrogatory to which an amended answer has been served may move for an order that the initial answer to that interrogatory be deemed binding on the responding party for the purpose of the pending action. This motion shall be accompanied by a meet and confer declaration under Section 2016.040.

(c) The court shall grant a motion under subdivision (b) if it determines that all of the following conditions are satisfied:

(d) The court shall impose a monetary sanction under Chapter 7 (commencing with Section 2023.010) against any party, person, or attorney who unsuccessfully makes or opposes a motion to deem binding an initial answer to an interrogatory, unless it finds that the one subject to the sanction acted with substantial justification or that other circumstances make the imposition of the sanction unjust.