This is super interesting! I guess in the example you gave "Y-Y-Y-You" is the most accurate representation because your stuck on the start of the word (which happens to be a capital), not continuing with new sounds if that makes sense. Then is the word was in the middle of the sentence with no capital it would be y-y-you because its just getting stuck on the sound, whatever it was. There doesn't seem to be that much stammering representation in books, but when it does pop up, I think it's great when they show more of the scope of stammering, not just repetitions. Even just adding elongation too (like "mmmmmmore" rather than "m-m-more") makes it seem more authentic, or including blocks.