FIRECalc balances are in nominal dollars, before inflation.
value of the S&P500 index in 1966 was 495. In 1982, it was 210. Real
dividends were $14.54 in 1966. In 1982, they were $11.92.
In nominal dollars, the S&P 500 index was 93.32 in 1962 and 117.3 in 1982. The dividends were $2.74 in 1962 and $6.66 in 1982. The CPI was 31.8 in 1966 and 94.3 in 1982.
The stock market's price increased very little in nominal dollars between 1966 and 1982. Dividends were a different story and that is why you see an improvement. But in real
dollars, the stock market went down, both in terms of price and in terms of dividends.
The data source that FIRECalc and others use is produced and updated by from Yale Professor Shiller. Dr. Shiller's web site is www.econ.yale.edu/~shiller/
. You can go directly to his historical SP500 data by using www.econ.yale.edu/~shiller/data/ie_data.xls
I think that John Bogle (of Vanguard) has drawn attention to this period in his books. I think that is why you hear mention of it so often.