After more issues than I can count with horribly inaccurate or just missing metadata from TVDB, I decided to switch to the OCD-friendly TMDB site/agent for my tv collection.
Thus begins my issues with properly pulling in content ratings. Initially, the oddness I was seeing, was the agent actually pulling content ratings (MPAA, like TV-MA, etc) from TVDB still. So I disabled the sub-item for TVDB, under the TMDB agent, under Shows.
After many debugging attempts as to why the rating was still stuck on the TVDB information, I found it was stale metadata xml’s in the show’s folder, under Metadata/TV Shows/a/2f2881c496c8e51cae78b4495eea3e8d316ea18.bundle/Contents. I decided to just unmatch the show, clear agent http caches, and re-match the show. Doing this, confirmed my longtime suspicion that Plex simply does not scrape content ratings from TMDB.
I am attaching proof-of-issue XML, for the overall information for the show Luther, which I verified to contain the proper metadata on TMDB (but not on TVDB). This file is located in: /mnt/user/appdata/plex/Library/Application Support/Plex Media Server/Metadata/TV Shows/a/2f2881c496c8e51cae78b4495eea3e8d316ea18.bundle/Contents/com.plexapp.agents.themoviedb
Info from TVDB, which contains more metadata: 0bin - encrypted pastebin
Info from TMDB, which is missing metadata: 0bin - encrypted pastebin
DEBUG logs from this issue: Plex Media Server.log (5.0 MB)
I highly suspect this is due to lack of updates from the PMS team, according to the GH page: https://github.com/plexinc-agents/TheMovieDB.bundle
Please do not say I should be using TVDB, unless you would like to incite an argument where I show you how much I’ve had to fix there versus TMDB 
