iTunes lost Artist, Album, and Genre info for 12,000 songs

Hi,

As noted tracks in .wav format don't hold tag information. This means that if, for whatever reason, the tracks are added into a new library all that iTunes can see is the filename. It will read this as the song name, complete with any leading track number if present, and assign the tracks to Unknown Artist and Unknown Album. If iTunes is also keeping the iTunes Media folder organised then the tracks get moved out of the folders that previous could have indicated the artist and album they belonged to. Without other details to go on I would assume that at some point you updated iTunes and it dumped your database, and you then allowed it to reimport the contents of your media folder, which would have added the tracks, but all as part of unknown artist/unknown album.

Is there a Time Machine backup of Harddrive-1? Do you know exactly when this problem arose? See Empty/corrupt iTunes library after upgrade/crash. It might be possible to restore a version of your database that contains the lost metadata. Given it is a Mac that restored database might even be able to find the files that have had their locations changed since this will all have happened on the same volume. If not I've developed some repair tools for Windows that I could try adapting for Mac. I'd start by using the Option-start-iTunes method to review each of the previous libraries one at a time until you find one that contains proper listings of your albums and artists. Once you've done that see if they play. Assuming they do we can then discuss how to put all of the components of the library into the best shape for future reliability, otherwise we can discuss how to repair the broken links.

tt2

With a Mac if a file has been moved/renamed within the same volume then the operating system should be able to locate the file correctly, so the fact that files have been moved might not present so much of a problem for the older library.

iTunes moves files and folders to reflect updated tag information if the Keep Organized option is enabled under iTunes > Preferences > Advanced. If/when you repair a broken link to a file that may not trigger reorganization, even for tagged files where updated metadata is recognised. Turning Keep organized off and then back on again can force all media items to their default paths. The "find other missing items" repair process seems to generally look for a single change in the folder path, so it is unlikely to work when content has been moved to Unknown Artist/Unknown Album.

You can find my general advice on organizing and moving libraries at Make a split library portable and Move your iTunes library to a new computer. You can manage multiple devices from a single library, however managing content from multiple IDs is slightly more complicated due to a feature called association. Details at View and remove your associated devices in iTunes - Apple Support. If your family uses multiple IDs then you might want to look at Family Sharing - Apple. You can copy non-DRM content from one library to another, however you want this in a tagged format (anything but .wav) so that you don't lose metadata. iTunes may not always play nicely with NAS. My recommendation would be to keep the working copy of the library on an external drive, cloned to the NAS as a backup.

tt2

It seems you have a split library. Read this User Tip by turingtest2 Make a split library portable