Asking tt2: add .itl to which iTunes library file?

It worked, but not perfectly. It allowed me to open the library, but does not include the songs added to the library over the past year. Curiously, the pre-converted "iTunes" folder confirms the songs ARE in the sub-folder "iTunes Music." They WERE in the library, but adding .itl which converted it to the new library structure, effectively produced the library as it was one year ago--less the songs added and the changes made to playlists. One workaround: With the newly converted (deficient) library open in Music, I can open Finder to locate each missing song in the original "iTunes music" folder and "open with" Music, which (re)imports it to the converted library. That imports critical files (name, album, date) but not all (composer, ratings). A pain because it will take time to find which songs are missing (among 4,000), and I will have to redo missing or changed playlists. Incidentally, the new library structure no longer has a "Music" folder showing all songs, which may be unfortunate.

If any of this sounds like i've missed something, I'm all ears. Thanks again for getting me this far!

Being loyal to Apple is also being dependent.  We spend years (decades) curating our music libraries—rating songs, creating playlists, correcting metadata (wrong years etc)—confident that our work will survive with each graduation of OS or iTunes/music app. 

That trust has been shattered.  

I’ve struggled for days to open old libraries in Music—reading and conversing in this forum, dutifully studying each link, following suggestions. I was successful only once, and even then about 20% of songs were “not able to locate.”  The maddening thing is that the songs are right there in the Media folder!  But one must find it for Music and “open with..(Music)” to reactivate the link. 

So the question remains, why does Music not open every song it the media library? No, it’s even more basic: Why can’t Music FIND songs that are right there in the Media folder!!?? (among songs that Music does “find” and play)  Forcing the user to find the songs for Music is simply a programming failure.

The good news is I have not lost any music. My advice: hang on to your old copies of Media/iTune Music folders!  Finder is the savior. Searching in Finder for a song reveals all media folders it is in (old library backups -path appears at the bottom of the Finder window) usually including the active library that SHOULD have found it.  It is irritating that I must Find and “Open with (Music)” to do what a half-brain software programmer neglected to put into each new OS or Music version to insure that loyal customers have seamless access to their data. 

Thanks to all who tried to help. There may be a better way that I never learned, but I have already wasted hours. 

Thanks! That did it!