Plex doesn't always find the correct metadata for a file, actually for my music it is all being indexed as the same band (we're talking 7000+ songs all being recognized as Delta Spirit, the file plays properly and is named properly, but the metadata shows the cover for the Delta Spirit album).
Additionally, I have a bunch of files not being indexed at all. A lot of them I realize are because on my computer I've set up my folders like this:
Movies
-Seen Movies
TV Shows
-Animated
-Comedy
-Drama
-Documentaries (I put movies and tv show documentaries in here)
So you'll notice that I have all my documentaries in my TV shows folder. This way when I add that folder to TV SHows in plex, it is now trying to match everything as a TV show, but some of them are movies. What can I do to make sure that files are being matched correctly, whether they are in the right folder type or not?