The survey has to be checked against reality. A job estimated at forty cubic metres that turns out to be sixty costs a crew an extra half day, and comparing the two afterwards is what makes the next estimate better.
A lorry without a crew is nothing. Vehicle, driver and however many porters are needed have to be assigned as one unit, and treating them as separate calendars produces a Saturday with two lorries and one team.
Photographs at loading settle everything. A scratch discovered at the destination is either pre-existing or caused today, and only images taken as items went onto the vehicle can distinguish the two.
The peak is predictable and finite. The last three days of every month and the summer weeks fill first, so knowing how much capacity remains there is what allows a company to price the rest of the calendar sensibly.