“Documentaries” should be the folder added to the TV show library.
If they are MP4 files and have incorrect embedded metadata, then that can cause Plex to incorrectly list the files. You can tell Plex to ignore the embedded metadata: Edit the library → Advanced → uncheck Prefer Local Metadata.
Suggestion: As a test, create a new TV show library and do not add any shows. Then, Plex Dance the Planet Earth show, but put them back into the test library. See if it correctly recognizes them.
FWIW, here’s naming & organization on my server. tv-docu is the folder added to the tv show library.
