In using Schwing's book for Model 42 research, I noticed that certain symbol numbers were reused for guns of different specifications at later dates. The same thing could have happened with Model 21s. A student of Model 21s can look at a gun and make a decision on originality without a Cody letter. I have never sent for a Cody letter before buying a Model 21. I just know, after studying and screwing with these guns since 1955 and owning and buying them since 1965.