I cannot find these files on my time machine to restore lost versions using your following instructions. Is this info. still valid, or has the location of songs and playlists changed since this 2013 (maybe now obsolete) post?

The file with the actual songs is here:
~/Library/Containers/com.massimobiolcati.irealbookmac/Data/Library/Application Support/iReal b/UserSongs.plist

and the file with the playlists is here:
~/Library/Containers/com.massimobiolcati.irealbookmac/Data/Library/Preferences/com.massimobiolcati.irealbookmac.plist