38 CFR § 20.1103
Rule 1103. Finality of determinations of the agency of original jurisdiction where issue is not appealed
November 5, 2020
A determination on a claim by the agency of original jurisdiction of which the claimant is properly notified is final if an appeal is not perfected as prescribed in §19.52 of this chapter. If no Notice of Disagreement is filed as prescribed in subpart C of this part, the claim shall not thereafter be readjudicated or allowed, except as provided by 38 U.S.C. 5104B or 5108, or by regulation.
[84 FR 191, Jan. 18, 2019]