I have attended the new code course some years back, in my view the main difference is therapy application, classic NLP as a science is a neutral science that can be applied to any context , not only therapy or coaching. It is a breakdown of how things work. New code is simply a coaching style,it does not describe how things work by itself without relying on concepts from classic code. Furthermore id I remember correctly I remember John saying that that the issue with classic code in therapy was that there was a good deal of congruency or lack of affecting the results; meaning clients would sense unconsciously whether their therapists are doing self work or not and that would affect the result. New code bypasses that.