The audit was not about finding the exact cause of the previous incidents:
The audit, which is kind of like a quality control inspection for large companies, analyzed 89 aspects of Boeing’s 737 Max production
The audit looks at current production to assess wether or not everything is being done to prevent further hazards (they failed over a third of the inspections). Determining what caused the past incidents would be assigned to the equivalent of crime scene investigators (FAA detectives?).
Determining production line compliance and investigating the cause of a major malfunction are two entirely different beasts.