UPDATE (and I felt like this needed it's own post): SUCCESS!

After adding KTN to his profile in my UA account, it didn't seem to change anything. But then I tried adding his passport via my account and it went through! All checked in. I don't know if it was bc I was adding it through my UA where I got the ticket or if it was bc my scan suddenly decided to work. But voila! AND the KTN is there and precheck on his boarding pass. We are good to go now. Maybe this will help someone else in the future.