Picked up my single biggest issue with iTunes when I did just that - extended the library to include a folder with thousands of sub-folders, all with organised mp3s of albums... [long story - but they are not illegal downloads!]... Some of them were obviously 'incomplete' for iTune's purposes, since I now have literally thousands of "Track 01's", "Track 02's", "Track 03's" etc...
All of them are listed as "Unknown Artist"... I've been ignoring them for a while now, but the pedantic in me is seriously freaked out about it... So much disorder!!
I'm hoping there's a better alternative than having to listen to each track, in an effort to identify it, and re-insert the details manually... :wtf: