duplicates do show but not from shows that are missing – some of the duplicates are broadcast episode and webisode showing as that same - which they are not
example of missing show is the youtube series TimeGhost - can be found in folders – moved a new episode to the folder old server found it (already knew about the series) but new server can not find it ?!?
It matched using the naming & organization shown below.
Some shows are a bit troublesome for Plex.
TimeGhost only has good info at TVDB. It is listed at TMDB under another name, “TimeGhost History,” and the listing at IMDB has no episode info. It is not listed at watch.plex.tv (which can indicate Plex Media Server will have trouble with it).
TV Show libraries default to TMDB episode ordering. If you still have trouble matching the show, try switching the library to TVDB. Edit the Library → Advanced → Episode Ordering.
If that helps it match, then edit the show () and choose TVDB Aired episode ordering (in Advanced section).
You should then be able to return the library to TMDB if desired.