Thanks for the clarification. Mea culpa. That 19% seemed too high.

Note the spreadsheet from Professor Damadoaran : http://www.stern.nyu.edu/~adamodar/pc/datasets/histretSP.xls

The years 2001-2020 inclusive S&P 500 arithmetic average inflation adjusted total return is 6.79% ( =average(o92:o111) ). Which is below the 1928-2020 average return of 8.5%. Inflation might be underestimated. 6.7 is a lot closer to your calculation!