If an entire iTunes library was purchased from the iTunes Store, all
the tracks came with complete metadata. Those lucky (and wealthy) users
can scroll through iTunes without seeing any jarring blank spots in the
Artist, Album, and Genre columns, or songs named Track 01 and Track 02.
The rest of us? Our multi-gig libraries were patchworked together from
ripped CDs, mixes from friends, tracks digitized from analog sources,
and, um, “found” audio files that could’ve come from anywhere.