I was just reading about the 2017-18 regular flu season that had so many record deaths. The CDC that year adopted some new way of estimating the deaths.
https://www.cdc.gov/flu/about/season/flu-season-2017-2018.htm
“In 2017, CDC began using new methodology to classify seasonal severity and applied the methodology to the 2003-2004 through 2016-2017 seasons. The 2017-18 season was the first season to be classified as a high severity across all age groups.”