Your data is far from complete in order to prove your point. You have 24 example over a period of how many years? Now copare that to the number of total teams combined in these years. Divide 24 by the number and you have a working percentage. Also, is the +6 game actually a turnaround? So a team 1-15 becomes 6-10. This is a turnaround?
The other problem is that you seem to think a turnaround is just having one good season.
- Miami Sparano went 11-5, 7-9, 7-9, 4-9 fired.
Todd Bowles went 10-6, 5-11, 5-11, 4-12, fired
Rat Mangini went 10-6, 4-12, 9-7, fired
There are other fake turnarounds on your list that will kill your stats and claims. You do show a good about of turnarounds, but you don't have 24 examples of a % of teams over the years it spans.