As you all know, you can see which files ( songs or vidoes) a certain playlist consist of, but it’s not possible to se which playlist or playlists a certain file (song or video ) are a part of already.
My suggestion is to add to the edit box where you can add tags and other info, a possibility to add, edit and delete playlists for that specific file.
There’s also an existing suggestion to manage the playlist association through tags (as per your suggestion)… there’s even 2 “flavors” of this
If that’s what you’re looking for, I suggest you vote/comment in those threads and we close this thread in order to avoid distracting/dispersing the attention (=votes)