There is no point having a reservation system that only handles what is reserved (i.e. planned) in the system. The system needs to actively handle real-life or it is of no use at all. In the rental business, you can be sure of one thing - stuff happens. Late returns are pretty normal and the system lets you keep track of who's returned and who hasn't.
The platform automatically detects late returns and mark those reservations with a warning.. Right now the system will simply mark the reservation with a warning:
[coming soon to BRM2.0] and it also stops late rentals 'disappearing off the radar':