I doubt that they can even go back to the 1983 decision because it wasn't appealed. He has to continue the appeal the decision through the appeal process BVA, CAVC, U.S. Court of Appeal Federal Circuit, and finally the Supreme Court. It doesn't take 35 years for the CAVC to hear his appeal of the BVA's decision.
He keeps on reapplying which starts a new date of entitlement. They are not going to pay him back to 1983 because he didn't appeal the decision.