Restored my iPod, lost songs.

Yesterday I had to restore my iPod touch, and most of my songs were backed up. However, it came up with a list of about 100 songs from my Purchased folder that would not be synced to the iPod. I assumed it would be all of my Purchased, and I could just look at a list in another place to re-download them. But as it turns out, it was only some of my Purchased, and from what I remember from the list, they were older purchases, not newer ones. How can I get a list of the ones it was forced to delete ?