Hello Randy ... I was searching everywhere for some help in getting this sort of thing working and came across your video and code here ... so, first things first ... THANK YOU ...
I am at the tail end of rebuilding a client's site from my initial build of it 7 years ago and needed a new way to recreate an immense hack I did back then to make this type of functionality work.
The scenario here is Artist and their subordinate Bio, Review, and Statement ... the goal is to go from the artist archive to their single tsa_artist post type template and then from within that template have all their subordinate pages listed. The sidebar stays the same throughout as an index to all things Artist.
The work you've done here is absolutely perfect, but, I'm running into a bit of a wall.
I have already created the post types ( I roll my own here ) and switched all the old posts to their appropriate new homes, prior to discovering that their was no way I was going to pull this off with many2many ... just keeping the artist's featured image/aka profile pic at the top of the sidebar looks impossible without resorting back to my 06 hack.
The steps I've taken thus far are to activate your code ... then comment out my initial registration ( registration only ... all my $args/$labels remain ).
The result is that everything appears to be okay, and I initially thought I could just delete the old posts and recreate them with the new thickbox interface so that the relationships would show, but, when I went to do that I noticed that all three metaboxes share the same name inputs etc. ... the Title is correct on all three, but, the inputs are all mirrors of each other.
I went ahead and attempted a test, and the post also showed up in all three metaboxes ... and my permalinks are set up fairly normal, but, the permalink to the test subordinate post showed it as being nested within a sibling subordinate instead of the parent ... in other words, the bio I made was inside reviews.
I know this is a book, but, I do try to be thorough~
I would love to send screenshots to show you what's happening here and stay in touch as I implement this tomorrow ( yep, have just one day to finish ) if you have an email and are available ... otherwise, any insight you may have on what could be happening here would be greatly appreciated ;-)