In all cases, foreign cars were used in preference to home road cars, if they were available. If no foreign car was available a home road car would be used. Determining how long to wait for an appropriate car was on a case by case basis. If shipper notified railroad he needed car on Wednesday and a system car was available Wednesday, but a correct foreign ownership car was going to be available on Thursday, would he wait? It was situational, some shippers where willing to wait a day or two, others, because of specific shipping dates for a product would specify that their order was date specific.
Car velocity was the most important item. Amount of money made on a specific shipment was not determined by ownership of the car. Carriers did not want to send their cars off-line unless no other car was available. Each carrier invested in their equipment and wanted it available for their own on-line customers. Once off-line the owner no longer had control of their investment.
Backhauling of empties over long distances was done in many cases. A good example was DM&IR in northern Minnesota had a large need for empty gondolas to load pulpwood and did not have sufficient inbound loaded gondolas to have sufficient car supply to protect the pulpwood loading. NP, GN, SOO, MILW, and CNW all delivered empty eastern ownership gondolas to DM&IR at Duluth. In many cases these were backhauled from Twin Cities to Duluth given to DM&IR. Once loaded the expectation was the railroad providing the empty would participate in the loaded eastbound move of pulpwood. Other examples are eastern ownership boxcars located in the Dakotas being backhauled to Montana points for eastbound grain loading. Backhauling was dependent on car shortages and time of need. Service Orders negated any backhauling of empties unless the Service Order applied to that need.
Keep in mind backhauling was driven by an agent having a car order from a shipper for a specific load to a specific destination.
If an empty PRR car was located at Roseburg on Wednesday and no load was available until Saturday, it would have been sent on its way towards home, possibly to be intercepted and used by another downline town if a load was available.
Supply of empties was dynamic. Each day at any given point there would be additional cars made empty that might fill an order at a specific town. For Car Distibutors and local yards this changed every hour.