Baggage car somewhat like Box & other freight cars would travel off line as needed from terminals. They were not exclusive to their home road although they spent more time there than freight cars. This would be likely due to the road owning fewer of them in the first place.
Heavy express shipments such as at [not allowed]mas time, season rushes, etc. might cause need for an extra number of cars above those normally available. Also special movements might require baggage cars such as a band, orchestra, or athletic team.
The archives has a record of at least one trip back in the 50's where the Metropolitan Opera was on a spring tour and they had at least two baggage cars of scenery plus extra Pullmans for the cast & crew. The trip portion of the tour over the Monon was from Greencastle to Bloomington then to Chicago. Stops were made for two nights in Bloomington and one night in Lafayette. (In my time there as an undergraduate I attended all of the West Lafayette performances.)
