29 CFR 18.53: Supplementing disclosures and responses.

(a) In general. A party who has made a disclosure under § 18.50(c)—or who has responded to an interrogatory, request for production, or request for admission—must supplement or correct its disclosure or response:

(1) In a timely manner if the party learns that in some material respect the disclosure or response is incomplete or incorrect, and if the additional or corrective information has not otherwise been made known to the other parties during the discovery process or in writing; or

(2) As ordered by the judge.

(b) Expert witness. For an expert whose report must be disclosed under § 18.50(c)(2)(ii), the party's duty to supplement extends both to information included in the report and to information given during the expert's deposition. Any additions or changes to this information must be disclosed by the time the party's prehearing disclosures under § 18.50(c)(3) are due.