This might be a good time to remind ourselves of what Annex 13 has to say:
"The difference between an accident and a serious incident lies only in the result"
Most AIBs operate on that principle, at least in theory, where as much attention should be paid to precursor events that didn't have a catastrophic outcome as to those that did.
In practice, though, a combination of public outrage, media pressure and lack of resources means that it's only the ones that kill a lot of people that get a 400-page investigation report.