Ok, I went to seat counter and search DTW-IAD with UA, UA like you said. I'm not sure what all the booking class means, so I'll give you what I found.

B--5; H--4; K--5; M--5; Q--4; U--5; V--2; W--2; Y--5.

I know it would be better if Y was 9, but what are all the others? Does that still mean there are quite a few empty seats?