Can you add everything to my liked songs without repeated songs?

So, I currently have 9166 songs in my liked songs, and 2 playlists: Music2 with 8794 songs, and Music3 with 8616 aongs.

My question is, is it possible to add all aongs from music2 and music3 to my liked songs to have wider library to listen to? And what happens if for some reason a song is saved like 3 times in a library the moment I want to add it to my liked songs? would it be saved only once?

thanks