As someone who spent much of my working life investigating 'failures' of newly introduced products, it is extremely difficult to determine when you have covered all possibilities and when you decide that there is no further information (which might contradict your conclusion) to collect.
It is only when you can predictably reproduce the 'failure' (which, by its nature was intermittent) that you can begin to be complacent.
By the nature of these Note 7 events, it is unlikely that much can be determined from examination of the remains - even if the evidence can be recovered and returned for examination.