Just as a side note 
What fixed this for you was adjusting the names.
The Plex Dance only helps Plex to “forget” it already knew the videos but had them mismatched as something else. Once a file has been added, Plex will recognize that file by a number of different criteria (file size / hash) – so if you change the name, it’ll figure that the name changed but it’ll ignore the fix because the file had previously been matched. What’s super annoying in your situation is quite a life saver if you fix some file names and don’t want Plex to identify the files as new items over and over.
