What are N and U classes on CO? I know the list says 'discounted coach' but CO *just* updated their website again when you try to book flights. It says...

Eligible for OnePass Mileage Upgrades *
(Y, H, K, N, or B Fare Classes)

Eligible for Most OnePass Promotions **
(Y, H, K, N, B, V, or U Fare Classes)