iPod Odd syncing problem - 5th gen iPod

Hi folks, I have a real stumper here. I'm trying to sync my old 60GB 5th gen iPod, which has been in a drawer for a few years, with iTunes on my 2012 MBPr, OSX 10.10.2. The problem is, only 155 songs out of my library of over 9k songs are showing up in the sync music window. I can't see rhyme or reason as to why these particular albums are there; some are old, some are new, some are from the iTunes store, some are imported from cd, and some are from Amazon. If I select a playlist with other music not in this list, it shows as empty. There are 11 artists (a small fraction of my library) but not all albums for the artists that are there. I've tried reformatting the iPod (using latest OS, 1.3), rebooting the computer, and cycling Manually Manage Music on and off, with no luck. FWIW I've been using iTunes Match with my iPhone 5s, so I haven't had to manually manage music syncing lately, but never had any issues like this before. Anybody have any ideas? Much obliged.