We ran a couple of state park CGs for two summers. one was a first come, first served and the other took reservations. Never had problems with the FCFS, but we did have a 'ace in the hole' site for those who came very late and were desperate. Very seldom ever used that.
The reservation CG was done through a reservation service and was subject to errors. We got reservation info via a computer where we printed the 'leaving on this date' cards. We kept a hole site for when the service messed up. This would happen, believe it or not. ;) If the site was not used by 6PM then it became available to FCFS. Many times, even after dark we had people coming in.
