Vehicles from pool and freight

[Karri]

The manual says that unit's supply detail window the vehicles from pool means following:
The number of vehicles received from the motor pool (after being converted from freight) along with the
percentage of need this represents

However, summing up all the freight it seems that this isn't converted at the unit level. Is it converted at the depot directly? Or is it not converted at all?

[Karri]

Also, with the above screenshot, the unit received 99 tons of supplies, but only 97 tons of freight. It also loses 43 tons of freight, so how exactly is that calculated into all this?