Wuhan recently tested all 9 million residents and found only 300 currently positive cases, which are not included in official figures since they are all asymptomatic. If they had tested the residents for antibodies instead then we would have a much better understanding of mortality vs immunity. So it seems like a wasted effort other than forcing residents out of their homes to stand in long queues. CFR depends on knowing the percentage of all cases, not just those showing up in distress at hospitals, as i suspect their official figures actually indicated.