What I was trying to say (albeit not very clearly), was that if you add /TV Shows to your Plex TV Show library, then you cannot have subfolders such as ~Documentaries underneath.
However, it is certainly OK to add ~Documentaries to a TV Show library, as it is the folder containing the TV show files.
Examples:
Not supported:
/TV Shows <-- Folder added to Plex Library
.../~Documentaries <-- Not supported
....../Planet Earth
