OK, here it is:
Timing Your Retirement
The basic flaw is comparing two people who start their retirement, at different periods, with the same amount of money. If your example compares two people who had the same amount, on a given date, but retired at different times, the results will be more valid.
Here's the original plot. The x axis is years from retirement.
Now, let's get rid of Betty, and replot it so the x axes are properly lined up:
Now the x axis starts at 1973. I've shifted Bob's line over, because he retired in 1975.
Now to extrapolate to see how much Bob had in 1973. Bill went from 750 K in 1973 to about 400K in 1975. So Bob must have had 1.4 Million in 1973 (750/400 * 750). The dotted green line shows that.