You are DEFINITELY doing all the right things. Have you read the book Explosive Child? It was through trying Plan B that I learned how very differently difficult child 1 thought. That revelation is what caused me to have him reassessed. on the other hand, because I realized that punishing difficult child 1 for skills he didn't have was like punishing a diabetic for having an insulin reaction. When I started putting my efforts into teaching those missing skills, I found I wasn't punishing very much and difficult child 1 and I were both happier.
As long as what you are doing is working, the diagnosis doesn't matter (well, it kind of does but...). The end goal should be improving difficult child's "quality of life" and making sure he learns the skills he will need to survive as an adult. Do whatever you gotta do, but only as long as it works.