Hey Jude (sorry!)
I was having exactly the same problem. I dragged one album onto my laptop and re-edited the tags with MP3Tag to see if it would work. It worked a treat so I dragged ALL the folders over to my laptop and put them all in MP3Tag at the one time thinking I could do it all in one fell swoop. When I put them all back on my player they hadn't changed! I realised that I would have to re-edit the tags one folder or album at a time. Did this, dragged them over to my player and they're all tagged properly now.
Just to make clear... when I say re-edit the tags I was just making some field I didn't need (like Album Artist) blank and then saving. The tags were already edited to my liknig, just not showing up properly on the player. Hope this works! Don't hesitate to ask any more questions.