I may be the wrong person to ask as I am pretty old fashioned. I never did the join-up stuff. Consistent (same signal means the same thing), humane handling while listening to what the horse has to say (and apologizing any time I irritated/hurt the horse), that is what I used.
Since I never "joined up" with any of my horses and kept pretty good relations with all my riding horses, I doubt if you would need to repeat the join-up. I consider it a tool to be used sparingly.
Nowadays I would consider using clicker training first before trying join-up.

Thanks for the "heads up" on about Ms. Goodnight. I actually googled her initials and through that found out who she was. I watched a couple of her videos.

I agree with what you said about Mr.Dorrance. Sad how some trainers can/will use the Dorrance name, to maybe attract people to them, but they do their own thing anyway.