Hmm, scary.
FYI, it took me a year to cross over from NAUI to TDI at the full cave instructor level. I had to:
1. Teach 3 TDI cavern courses
2. Intern with at least one intro course taught by a TDI instructor
3. Complete a TDI intro to cave IE.
4. Teach 3 TDI intro courses.
5. Intern with at least one complete full cave course taught by a TDI instructor, and receive a written recommendation to proceed onto the IE from that instructor.
6. Complete a full cave IE. The IT was not allowed to be the same instructor that recommended me to go on to the IE.
Pre-reqs to begin the process were full cave certified diver with 100 non-training cave dives (for cavern instructor), 150 non-training cave dives (for intro instructor), and 200 non-training cave dives (for full cave instructor), plus of course OW scuba instructor having taught a number of courses. I believe I had around 800 non-training cave dives when I started the process, but I stopped keeping a logbook back in 1998.
Now.. I've done quite a few more internships than was required for the minimum, and I guess it is possible to have progressed faster than a year. I believe I've now worked with a dozen different cave instructors with courses for all levels. But, I don't see how someone could have become a full cave instructor from nothing in the course of a weekend with TDI.