For me, those are perfect examples..... I do not remember the fine details around either event. The actual events, certainly but not the entire time frame around them. And I was both alive and adult for both of them :-) But I do remember extraordinarily small details and the entire time frame around the events of 9/11- maybe about one- half of that day, starting when I was told that it had happened.
Not saying you are wrong or even disagreeing with you here, just saying that that particular day, 9/11, is etched into my memory along with a number of hours surrounding it with amazing detail and in correct chronological form rather than snippets or individual images. I remember the two events you mention in more like 3 second 'clips' and not in chronological order really.
I think the reason for this is that those particular events (9/11) were outside the perceived area of possibility while the other events were not. Extremely dramatic, sure but not beyond what could be imagined (Reagan being shot and the Challenger explosion). On the other hand, it was inconceivable to me that <anything> short of a large nuclear weapon could actually
knock down one of those buildings. In fact, I still believe they are, or would be, immune from actually being driven down by any outward force; they of course actually collapsed due to several floors suddenly giving way and causing 'pancaking' of the upper portions of each building.
Brian
Or when Regan was shot, or the space shuttle exploded. Highly emotional and/or traumatic events tend to strengthen the memory pathways of the brain. It is a natural survival trait, and one shared by other animals, too.