Good point; I missed that nuance.

If the only thing that happens is that a one-class plane is replaced with a two-class plane, I wouldn't expect to be put into F. After a schedule change, I can see it both ways. Positive space rebooking, yes, but also OP was in Y on the affected segment.

It does increase my confidence that HUCA (and not escalation) would eventually have worked, as you suggest.