That one mere fact changes the whole philosophy of the investigation - there aren't any 'holes in the cheese' to line up. It appears to have been a singular cause, by a singular act. Thankfully, an exceptionally rare one (as per my previous post);.
I know what you mean but beg to disagree.
You could argue that in this case one of the holes in the swiss cheese was mandating locked cockpit doors in the first place.