To continue to develop. And I don't think he "thought he had The One True Path" either. I don't know how you are coming to that conclusion.
I was in a small group of trumpet students at Univ of North Texas gathered by Claude to look over and comment on his "Systematic Approach" that was still in manuscript. I got the impression that he was putting something down that would be a one-source (sort of) method for growth. I got no impression that he was dogmatic.
Additionally, he seems, like all great teachers, to have tailored his private lessons to his students, something you just can't do in a printed volume. In which case, you have to have some insight into the fundamentals of his approach and then apply common sense.