Why is there a big discrepancy on reported US deaths?

Following new CDC guidelines: "As of April 14, 2020, CDC case counts and death counts include both confirmed and probable cases and deaths. This change was made to reflect an interim COVID-19 position statement issued by the Council for State and Territorial Epidemiologists on April 5, 2020. The position statement included a case definition and made COVID-19 a nationally notifiable disease.

A confirmed case or death is defined by meeting confirmatory laboratory evidence for COVID-19. A probable case or death is defined by i) meeting clinical criteria AND epidemiologic evidence with no confirmatory laboratory testing performed for COVID-19; or ii) meeting presumptive laboratory evidence AND either clinical criteria OR epidemiologic evidence; or iii) meeting vital records criteria with no confirmatory laboratory testing performed for COVID19" [source]

This change is a further example of one of the many reasons why the label "confirmed cases" (used by some to designate total cases) is incorrect (see definitions for more details). The US CDC (and Worldometer) has always used the label "Total Cases." Canada is another example where the "total number includes publicly reported confirmed and probable cases [source]

On April 14, New York City reported 3,778 additional deaths that have occurred since March 11 and have been classified as "probable," defined as follows: “decedent [...] had no known positive laboratory test for SARS-CoV-2 (COVID-19) but the death certificate lists as a cause of death “COVID-19” or an equivalent" [source].

https://www.worldometers.info/coronavirus/us-data/