The asset and the agreement are different things
A rentable asset exists independently of any agreement: it has its own identity, condition and history. The agreement says who holds it, from when and until when.
The separation matters because the same asset passes through many agreements, and "where is it now and when does it come back" needs an answer without opening agreements one by one.
Availability, from the same engine
What is free is computed with the same rules as hotel reservations, appointments and events — including cancellation and deposit policies. There is no second way of deciding whether a period is taken.
Worth knowing
In a rental business the money is lost on return, not on handover: an asset back late, one returned damaged, a deposit not withheld. That is why an agreement has a term and a state, not just a start date.