All my coach United boarding passes show Y class even if they are K, V or any of the other discounted fares. When I upgrade it shows F or C for Business on 3-class planes.

TWA used to show the same thing on the boarding pass, either Y or F no matter what the fare class paid.

As far a the E+ seating they do open those seats up at the airport, so a non full coach paying customer or a non Premier can get a E+ seat at checkin.