What is the difference between a Renshi, Kyoshi or Hanshi? You might as well ask what the difference is between 6th, 7th and 8th Dan. Small difference between them in terms of time and experience. No great leaps of ability. Getting to the first level, Renshi, is a many-year development that was most likely never even a goal.
Someone once told me years ago, "Renshi means teacher of teachers." Who teaches the black belts; who helps them to new understandings? Who helps 3rd and 4th Dans find more of their own unique abilities and helps them to see the art growing in themselves? Who builds the bridges to the future students who are not yet born? I never really thought there was a difference between Renshi, Kyoshi and Hanshi that could even be tested or seen. It seems to be more age and experience than requirements and an outline on a piece of paper. Like listing the feeling of looking at a sunset, or feelings for a brother, or what's in you the thousandth time you do a kata.
I think in America we try to define and list everything. Yet some things defy description. Like what does the wind look like, or the effect of your child's cry on your heart?
After 27 years in karate, I'm not much at reading karate books (I only bought one; guess which). The only thing I like about meetings is the end. I sometimes forget the names of techniques. I don't write letters for beans. I don't really care what rules we had ten years ago, or ten years from now. In ways I'm a sorry leader, but that doesn't bother me much.
I do know how to open doors in karate. I know how to make you think if you've been in three months or ten years. I can make you wonder about why you do things, or why you don't. Make you examine yourself and prove the way you think about karate or change. I do know the spirit of karate is in me. And what I understand about karate I carry inside me on no list, and I pass those understandings on to others for the future.
With invisible hands I write on unseen spirits of people who carry karate into the future. I only try to teach black belts to teach themselves. Then they can learn what hasn't been taught to them, and they are then prepared to find what's new that our own teachers didn't know.
The teacher should lay the blocks of knowledge and understanding so the ones after him may reach higher. If this is what a teacher does, then I have truly taught. Perhaps even without a list of requirements, you may understand a little better what Renshi, Kyoshi and Hanshi are.
Look with your heart also, not just with your head.