The unreported cases are included in the Infection Fatality Rate (IFR). The Case Fatality Rate looks at how many have died against how many diagnosed cases there are. The US CFR is currently 1.8%. To get the IFR, serology studies (antibody testing) and other data is combined with the case numbers to calculate a total number of actual infections. The deaths are then divided into that to get the IFR.
So the Case Fatality Rate is 1.8%, but that misses a lot of asymptomatic or mild cases. The Infection Fatality Rate does account for those missed cases, and is 0.65%.
How can those “missed cases” be tabulated? By their very nature they’re never reported. If estimated, how are accurate estimates of missed cases determined?