[oldalum]

If, for whatever purpose, you want to make some other estimate different than CFR, you're free to do so.  But, the 4.0%, 3.5%, and 2.3% are measures, not estimates.

To be precise, they are measures that are being used as estimates of the true CFR because they are the best information we have. In this context, the term "estimate" is a statistical term: we are using a measured value from a sample of a population to estimate an unknown population parameter. The true population parameter is the item of interest: what can we expect the case fatality rate will be if the infection spreads among the general population in specific areas/countries. The information you provided from WHO explains why the current sample is inaccurate and the (sample) CFR will change over time and become a better estimate of the true population CFR. And a population's CFR, as has been pointed out, depends on the unique age and illness distribution of that population as well as its health care system and resources.

[oldalum]

If, for whatever purpose, you want to make some other estimate different than CFR, you're free to do so.  But, the 4.0%, 3.5%, and 2.3% are measures, not estimates.

To be precise, they are measures that are being used as estimates of the true CFR because they are the best information we have. In this context, the term "estimate" is a statistical term: we are using a measured value from a sample of a population to estimate an unknown population parameter. The true population parameter is the item of interest: what can we expect the case fatality rate will be if the infection spreads among the general population in specific areas/countries. The information you provided from WHO explains why the current sample is inaccurate and the (sample) CFR will change over time and become a better estimate of the true population CFR. And a population's CFR, as has been pointed out, depends on the unique age and illness distribution of that population as well as its health care system and resources.