Nobody knows the true rules yet. If it was me, I’d HUCa more than once if needed.
they could be right. Did they say why? It could be the implemented according to Noble’s outline of how it should work, due to the availability of just AUS-PHL as a married segment. Or it could be clumsily implemented and because there isn’t availability AUS-PHL-LHR (probably because you are already holding the award space they intended to release and there won’t be more until perhaps last minute.