I have both manually in finder (in music folder on ext HDD), manually in iTunes, and have run Araxis duplicate finder multiple times. When I have gone thru 120+ gigs of music (whole family's) folder by folder, I make sure itunes isn't running. Then I open and sync. There's roughly 18,000 songs, videos, iTunes Extra stuff (moving itunes extra stuff and videos to another folder). But iTunes Match says I have 13,000 + songs but I would say 1/3 or more are marked duplicates. How do I get those to clear out. There is no other copy of a song on my hard drive. I even took off the copy to iTunes folder and organize files because that's where I have found duplicates occur. Or do I delete the whole library (library file) and start from scratch. My song counts are off too. I got a MacBook Pro and an Air and somehow the counts and last played also are screwy because I listen to my iPhone or iPad every night as I sleep.
Thanks in advance
Suggest that you use home sharing to transfer files that are not on your MacBook Pro from the Air. Once you've got them all on the MacBook Pro allow to up date.
Next use iTunes Match to show those with an Icloud Status as "duplicate". If you are happy that they are duplicates, delete them from your library. Next use iTunes to find exact duplicates. Under menu > view > you will see find duplicates - if you hold option key this will change to "find exact duplicates". You can now delete appropriate version.