David Splinter (Joint Committee on Taxation) has posted The Distribution of Capital Gains in the United States: A Comment:

National income is estimated based on a consistent treatment of economic income flows. Research on the distribution of income (Piketty, Saez, and Zucman 2018; Auten and Splinter 2024) uses these agreed upon national income concepts. Notably, national income excludes accrued capital gains, as income is only generated by an underlying asset when it contributes to current-year production. Capital gains, in contrast, are based on volatile asset-price changes and are not meaningful measures of economic income. Adding capital gains to national income breaks the consistent approach to income measurement, shifts capital income forward in time, and exaggerates top income shares. This comment reviews the Campbell, Robbins, and Wylde (2024) approach of incorporating capital gains into national income, challenging their analysis, conclusions, and contributions to the literature.