Why doesn't my classic iPod show all of the artists songs any more?

My classic ipod won't show all of my previously purchased music nor everything I added to my library from my own CDs. It's not everything, just the music I listen to the most. My PCs and iPad are all authorized via apple and I have never had issues with my ipod before, but I am now running iTunes 12.01.26. I even reset it to factory specs and started over - same artists that show up with 0 songs even though I have lots.