Rush Studio Albums 1989-2007

I am using Itunes 12.1.2. My iTunes runs off an external Seagate drive. Windows PC running Windows 10. I imported into iTunes RUSH Studio Albums, which is 7 disks. However, I did not import disc #5 because I already had that. My problem is that discs 1-4 are grouped together. Discs 6-7 are grouped together. Why can't they be grouped together 1-4 and 6-7. Is Apple Itunes reading disc #5 a part of that set somehow?!? I have checked if the album names are different (slightly). It does not appear so. Help?!?!