On January 1 1999 the USA switched from ICD-9 to ICD-10 for reporting mortality. (ICD-10 was not used for non-fatal clinical coding until 2015.) And as with all new things, morticians likely stuck with the more generic codes from ICD-9 and gradually started using some of the more specific iCD-10 codes over time. ICD-10 has 55,000 different codes compared to 17,000 codes available in ICD-9.

Could the gradual adoption of a more granular coding system in 1999 explain the increase in reported deaths due to falling that starts in 2000?