Here's another well-known example.
Bill Rodgers Early Marathon Progression:
- April 1973 -- Boston Marathon (Did not Finish)(DNF)
- October 1973 -- Baystate Marathon (2:28:12)
- April 1974 -- Boston (2:19:34)
- April 1975 Boston (2:09:55) 1st American Record (AR)
Two years from DNF to 2:09:55; eighteen months from 2:28:12 to 2:09:55. That's much more impressive than improvement from 3+ hours to sub-2:45 in nine months, whether by man or woman.
But really, there are lots of less well-known examples from a wide range of runners.