Mad Scientist
I think that the Agencies interpretation is that the fleet need to be grounded if there is 1 every 1.000.000 FH possibility that the problem leading to a catastrophic event can happen ; it is obviously not necessary to wait and see if the catastrophic event happens.
Reading the thread, it seems to me that many similar occurencies already happened to many of 330/340, and maybe, by pure luck or lack of coincidence of other events, those occurencies never became a 'catastrophe'.