REMOVED

Did you try manually copying the Music folder from your Time Machine backup to your home directory?

Also try navigating within Finder to the TM Backup and locate your music folder and see if the your music is there.

It should be in Music/iTunes/iTunes Media/Music

I had exactly the same problem , some music files gone with the jpegs in place
there is something strange going on here
Luckily for me I always have 2 backups , one onsite with time machine and one offsite with rsync
in this case I would have been screwed relying on time machine

no matter where I look on the backup drive , oldest back to newest backup , everywhere are the same files missing
now I formatted the backup drive and made the backup again from scratch and everything seems fine again

In my case it's because I excluded "Music" in Time machine... my mistake....