The broken ankle is an example you don't like, how does a route find nightmare that forces you either walk out exhausted to meet a date on a permit. I have spent the extra night in that circumstance. I always have enough food for another day or two.
An exit date is only important, if you don't tell your family you have changed the date, since the forest service does not require you to close the permit. Same goes for itinerary, if you change it between you ranger station and the trailhead, it is more important to tell your family than the forest service since they are one's calling the sheriff's office.
The permit system is one of voluntary compliance. Our trails are not patrolled by people with police power on the whole.
