I'm still dubious of your claim that "many" stutterers achieving your type and level of fluency. What's many? 30 percent? 40? 50? I'm willing to bet it's much lower; people who achieve your level and type of fluency through therapy. If it was that high, I think there wouldn't be a constant statement in any stuttering pamphlet saying the likes of, adults do not grow out of it, or, there is no cure. However, I do think there is another sizeable group that achieves pseudo fluency by avoidance, substitution, other covert behaviors, etc etc. But that discussion is going down another rabbit hole.