I myself am a fellow zune user (not much of us left I think)
I will say .. it really depends on if you bought the music from Zune marketplace . or you still have it on your computer.
Upon instailing the New version of Zune, the program probably searched for your music files and added them to your collection.
If you know for sure you deleted those files a while ago, and you sighned in using your Zune Pass / Zune account.
The software could have uploaded your old songs.
How do you lke the New version of Zune , compared to what it used to be ?