claim of CUE is a collateral attack that can only be made on a final RO or Board decision, see id. at 1380-81, and generally, rating decisions by the VA are deemed “final and binding ... as to conclusions based on the evidence on file at the time the VA issues written notification” of a decision, 38 C.F.R. § 3.104(a). In cases of grave procedural error, however, the Court of Appeals for Veterans Claims has consistently held that RO or Board decisions are not final for purposes of direct appeal. See Tablazon v. Brown, 8 Vet.App. 359, 361 (1995) (concluding that “where VA has failed to procedurally comply with statutorily mandated requirements, a claim does not become final for purposes of appeal to the [Court of Appeals for Veterans Claims]”); Hauck v. Brown, 6 Vet.App. 518, 519 (1994) (<HOLDING>); Kuo v. Derwinski, 2 VetApp. 662, 666 (1992)
holding that where va never sent the claimant a formal application form pursuant to  3155 the oneyear time period to return it could not have begun to run and therefore the effective date of the claim was the date of the informal claim holding that a notice of claim period did not begin to run until discovery of the injury holding that where an appellant never received notification of any denial  the oneyear period within which to file an nod which commences with the date of mailing of notice of the result of initial review or determination did not begin to run holding that oneyear period commences on date of discovery of the fraudulent nature of the transfer holding that the time in which to file a petition for review of a commissioners order commences upon the signing of the written order