PRR removed the bus bars from the ex Great Northern electrics that they bought in 1957. All of the Reading MU motor cars had a pantograph.
Jim, you are correct. All Reading motored cars had pantographs and no traiers except the RPO did.
Another reason for not using all pans in a train. By not raising the pan on the first motor car, the train may be able to move on in case of a wire problem that damages the pantograph, allowing seervice to be restored quicker. Similarly, most electric locomotives have two pans, with the rear used normally.