It came from topLingo's blog ...

I may have figured out how  Lala works their licensing mystery.  When synching your music collection, the service somehow matches mp3 tags like artist, album, and song title.  I think song length may also have something to do with it.  If it finds an “approximate” match AND the song is licensed for Lala’s use, the song gets dropped into your online music collection.  I bet this is somewhere in the FAQ on their web site, but I never read that nonsense … do you?

Why did I only find this out 6 months after I started using Lala?  Very good question … glad I asked it.  It takes forever to upload songs, so I only uploaded the first 20 gigs of my music collection.  I never processed the whole collection because I have 500+ gigs of music.  Because of how I originally converted all my CDs, my music collection is organized in an odd manner.  It’s very complex, but let’s just say I uploaded the most mainstream music first.  All my music matched and so I blissfully used Lala for 6 months.  Now that I am so enamored of Lala, I’ve decided to upload the rest.   Much of this current music that I am uploading is eclectic and indie.  So it’s not really matching.  See, I may be uploading a live or demo or rare version, and Lala mismatches it with the production studio version of the tune!  If it doesn’t match, Lala omits it from the album entirely.  This isn’t so bad, except you don’t know until you go to play an album and the last track isn’t there or track 5 is not what you’d expect or way too loud compared to the rest of the album.  I’m obsessive about music and my spidey sense tingles when something is out of whack.  However, I breathe deeply. count to 10, and then move on.  Oh … the other issue is that on CDs with unnamed hidden tracks, I’ve edited out the silence and re-saved the track under a new name.  Green Day’s “Dookie” has that with the “All By Myself” song.  Lala doesn’t recognize this sort of thing.  Bummer.

So consequently, my Lala collection is incomplete and mismatched.  Probably 10% of my Lala collection is askew.  I have an enormous quantity of weird music, however.  So although my OCD has been tweaked a bit, I am willing to overlook the slight problems in favor of the enormous convenience.  For the great majority of the population for whom Meatloaf’s “Bat Out Of Hell 2″ (you know “I’d do anything for love, but I won’t do that!” … you have it on your iPod and you LOVE it) is the weirdest thing in their iTunes, this won’t matter.  All the Kanye West, Christina Aguilera, and Black Eyed Peas that you need is covered with Lala’s library.  Enjoy it!