No. Junior black belt is only for children under 15 (don't hold me to the exact age). When I test for black belt in my current organization, I'll be a full-fledged 1st dan.
I've heard of some karate schools with a Shodan-ho. I'm lead to believe this is a standard probationary period.
My former organization had 3 brown belt levels. A solid brown belt, a brown belt with a black stripe through it (like the white stripe on a junior belt), and a half brown/half black belt. The half brown/black belt was the final belt before black. I didn't learn any new material during that rank. It was a minimum of 6 months of consistent training and refining my skills before I tested for black belt. My current organization doesn't have that, but the amount of time between advanced brown belt and black belt is 1 year, so realistically it's the same thing minus the additional belt.
Edit: I forgot to insert Photon's last post in this post and can't insert the quote now.