I think what Advance is trying to convey here is that Airservices' SMS procedures should ensure that any single ATC system component failure should not result in the need for implementation of any reduction in airspace utilisation or capacity to maintain aviation safety. The fact that Airservices had to resort to implementing limits on traffic handling capacity indicates that their SMS approach had failed and that, in order, to continue to maintain adequate safety, traffic handling limits had to be imposed as a last resort. The question Advance is really asking is what was the level of safety available to in-flight pilots between the time the failure first occurred and the time that the traffic handling limits started to become effective.