Im not sure how academic this is, but when I was in speech therapy over a decade ago, my therapist said there were 3 main types of stuttering. You’ve said basically the same here but he had different names. 1. A repetition stutter, “R-r-railroad” 2. A prolongation stutter, where a sound is held for too long “Rrrraaailroad” 3. He called this a “stop and start” or a “block” where the sound seems caught in your throat but doesn’t come out “r……ailroad”