Can you put 1 song in more than 1 Playlist
Obviously yes 
I was doing it anyway just making sure.
Yes the thing to try NOT to do is to have more than one copy of a version of a track on drive. Then you can put it in as many playlists as you so wish. By having more than one copy then you run the risk of setting a cue or loop on one copy and not having those on the other copy(s)