Know whether a song is used in any playlist(s)

I would like to know whether a song is used in any playlist(s). forScore has this feature.

My library has duplicates of the same song with numbered names or slightly different names.
If I look at my song list and delete a duplicate version, I don't know whether it's going to disappear from a playlist. Often I have a preferred version (sometimes I've made my own chart of a song), so I'd like to be able to use that version in any playlist the song is used. But there's not an easy way to know which playlists a song is used in.

We understand the problem :)
You can create a Setlist for the relevant playlists, then use this to compare, and you know the songs to replace if you need to.
As a precaution, share each playlist (in iReal Pro format), in case you need to rescue a song in one of them for some reason.
A screenshot of the song with the Player controls showing might be useful, so you know what style, tempo, key it is in for that playlist.

Then for the duplicate songs, you can compare them from the Song library, (swipe, next, previous) so you can see if you want to keep any or reduce duplicates to just one.
Then you have your Setlist with the key once you have added it in.

We hope something here is helpful, thank you for your suggestion :)

@dflat I have the same issue as the OP since I get sent numerous playlists from many different people or for different gigs, I often end up with duplicates.
Also it would be useful to know which playlist a song is in as it would help me to work out who sent me each song.
Also when creating a playlist myself it would be useful to see if a particular tune is already in my playlist so I don’t try adding it again.

I don’t see that your suggested solution would help for these things (although thanks as ever for suggesting!) - what would be really useful would be if when you click on Add to Playlist, it brings up the list of existing playlists, if there was a small tick next to the playlists that song is already in.

Would that be possible to add?
Thanks!

I don't know if this can help, but when you're inside a playlist, you can add songs directly in it. There's a search function that can display all the songs from the main library except the ones that are already in the playlist. When adding songs, if you can't see the one you're looking for, it means it's already in the playlist or it doesn't exist in your library.