I would think. And if that proof exists, it will come up at the appropriate time during legal proceedings. I'm skeptical there is any.

I guess they could call the entire existence of GARM to be collusion; companies banding together to "punish" companies who don't follow their guidelines. But X is (was?) a voluntary member of GARM, so it seems that would be a difficult argument for them to make without implicating themselves too.