BXP1 cannot be used on fare codes S, N, O, G and Q.
G is definitely good for BXP1s. I think it's the lowest inventory bucket that is good for BXP1s. I know this because many of my GSA (government/military) tickets book into G and it's one of those rare instances when I cannot use a SWU but a BXP1 works fine. -FlyerBeek