The legacy scanners are no longer receiving bug fixes or feature updates. They will be discontinued at some currently unspecified date.
The Plex documentation on how to name movies and TV shows has been consistent over time (reference). Other formats may or may not work. If they do, you’re basically getting lucky. If you follow the documentation, the media will be matched and correctly added to the library the vast majority of the time.
If a show using undocumented naming is currently matched, it will most likely stay matched. However, if the show is added to another library or moved to another server, it may not be recognized unless renamed.
As mentioned above, there are many tools, some free, to assist with any needed renaming. They can make short work of renaming even large media libraries.
