Never stayed late, never arrived early, unless it was like ... 15 minutes early or something like that.
However, we have on several occasions over the last 35 years run into the situation where one of the neighboring campers had multiple vehicles on their spot and used our campsite as a parking spot. And then there's no one around to move the vehicle. Yep, that's happened a few times.
FYI, Indiana State Parks has cracked down on that practice by the way. I'm amazed how, all this Summer, and every park we've been to, they screen ever vehicle coming into the campground, and actually enforcing the, only one vehicle per campsite rule. Of course, it makes for long lines at the campground gate house too. But I'm glad to see it.
What's really bad though, is when you find yourself in a different time-zone than home and all of a sudden you realize you have one hour less to get off the site. Been there, done that too! But me made it!