Excess mortality is the number of deaths from any cause that both occur in a given time period and surpass the expected number. Deaths in the United States have been carefully counted for more than a century. These “all-cause mortality” numbers are extraordinarily stable. We know to a remarkable extent how many Americans are expected to die every day.
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Excess mortality does not depend on counting the number of covid-19 deaths, which ultimately relies on the subjective opinion of physicians and medical examiners proffering their best guesses on death certificates (and whose minds might be understandably steered by the day’s news — “Did this patient with advanced cancer die of the coronavirus, or with the coronavirus?”).