If Plex isn’t adding the files at all, I suspect a permissions issue. This guide should help:
Configuring Plex to use embedded tags is a different question. I was frustrated for years with the poor state of the online databases, long before Plex came along. So I keep my embedded tags in good shape. You can set Plex up to prefer local metadata, but Plex will still check online sources for information it doesn’t find locally. Check this How-To:
[HowTo] Configure Plex to use embedded metadata (music)
With my tags in good shape, and Plex configured correctly, I’ve found it to be pretty reliable. When problems arise, I can usually attribute it to mistakes in my tags.
One caveat: If you’re working with classical music, Plex has some issues, because it doesn’t support all of the tags that are necessary to handle classical. This feature request has a detailed explanation of the problem.
