Transportation - Question on Routes thru' weight groups

Hi Sappers.

It appears the weight groups usage for route determination works only in deliveries, not in orders? If so, then potentially, the route will differ in the order and in the delivery which can affect the ATP considering different routes will have different transit times thereby, the delivery date coming up in the order will be unreliable/incorrect?

Is my understanding correct or is there any way around it so that the correct route on the basis of the weight groups does get selected and does not change in the delivery (keeping the delivery type as not allowed for route re-determination)?

Thanks a lot.