I give up with you lot. You are trying to apportion cause and blame when it is impossible to know the reason why those aircraft collided. There are always contributory factors, which when put into the chain could (but not do) lead to an accident. This is exactly what the Chinook issue digressed into and we still do not know whether that one was purely pilot error (they were grubbing it) or there was a deeper problem with the aircraft.
Most of what you are talking about is "engineering" airworthiness but of course there is much more to it than that. The fact remains that the crews were aware of the airworthiness limitations of their aircraft, including the fwd HISL issue and presumably took these into account in their flight planning and profile - we shall never know.
I recall hearing the tale of a Wasp pilot who, when night flying in the vicinity of his ship thought the aircraft was on fire. After the subsequent ditching his crewman asking what the h**l he thought he was doing. Turned out it was the anti-coll light reflecting off some cloud! Airworthy or not?