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The fact check page you provided seems clear that as early as March 5, 2020 (when the fact check was published) experts believed and were stating publicly that the IFR was not 3.4%:

> A Feb. 28 editorial in the New England Journal of Medicine, co-authored by Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, took the position that the mortality rate may well fall dramatically. It said if one assumed that there were several times as many people who had the disease with minimal or no symptoms as the number of reported cases, the mortality rate may be considerably less than 1%. That would suggest “the overall clinical consequences of Covid-19 may ultimately be more akin to those of a severe seasonal influenza,” the editorial said.

There are many similar lines.