Everything Veterans Affairs does with your service connected disability compensation claim, is governed by law. You may want to bookmark this page as a reference as you proceed with your claim. It can be a bit daunting. Just remember the U.S.C. is the law, the C.F.R. is how they interpret the law and last but certainly not least is the V.A. adjudication manuals that is how they apply the law. The section of the law that covers the veterans benefits is Title 38 in the U.S.C. in the C.F.R. is usually written 38 C.F.R. or something similar.
United States Code is the law and the U.S.C. is the governments official copy of the code.
U.S.C.A. contain everything that is printed in the official U.S. Code but also include annotations to case law relevant to the particular statute.
The C.F.R. is the interpretation of the law.