38 CFR §20.1400

1. (a)Review to determine whether clear and unmistakable error exists in a final Board decision may be initiated by the Board, on its own motion, or by a party to that decision (as the term “party” is defined in Rule 1401(b) (§ 20.1401(b) of this part) in accordance with Rule 1404 (§ 20.1404 of this part).
2. (b)All final Board decisions are subject to revision under this subpart except:
   1. (1)Decisions on issues which have been appealed to and decided by a court of competent jurisdiction; and
   2. (2)Decisions on issues which have subsequently been decided by a court of competent jurisdiction.