Yep, they’re all turning up now. Takes a while to scan, but this is the core problem solved. It seems that organising series into folders is possibly necessary for your sanity as they aren’t sorting too well, all in one folder, but that is the extent of the issue wrt exact naming conventions. Whereas my discipline to use names that sort perfectly in a DOS naming way is apparently superseded by some other priority that I am yet to get to the bottom of, but all perfectly visible pathways to sort it.
So my core defect was putting tv files in a movies library. The Plex dance, as stated, wouldn’t have worked. For anyone else making my mistake, what you need to do is rename the problem directory, delete the Library in Plex and just make a new one using TV shows, name it what you like and point it at the renamed folder. That is enough to fix this mess as the original folder cannot be recycled in the way described as ‘type’ is locked.
