Many of the engineering decisions were judgements and interpretations of descriptive requirements; the critical aspects were not clear-cut 'yes/no' choices. Many levels of the certification process could have thier 'say'; who were these people, what was said, why … hard evidence of a 'soft', fallible human judgement - difficult to identify, if at all.
Much of the judgement depends on engineering expertise, but its not clear if this was generally lacking (manufacturer and regulator) or specifically about the 'old' 737, its precedents, and justifications.
Judgements on the Max could have been made based on recent experience of modern aircraft, and this could bias retrospective application to older aircraft, particularly previous versions of the 737 with a history of judgmental changes, e.g. trim wheel, yo-yo manoeuvre, crew reaction time.
Its difficult to learn from that which is not known. Time might tell, but meantime the industry needs expertise at all levels, reliable processes of double checking - manufacturer and regulator, and management commitment to safety.
Unfortunately identifying 'need' does not ensure 'gets'.