So if I flip a coin and get heads, then I have enough evidence to say heads will land a large majority of the time? Haha, no. Sample size is important. Not to mention, successful NFL coaches aren't leaving for college jobs.
You are also choosing to mention that college to college coaching changes very rarely work as well.
This is why, IMHO, an AD has to be an excellent interviewer and a great judge of talent. You can't limit the search pool.