When SA began the "outsourcing program" of the lower-cost 'glas cars, they had been sequentially in the 4300 numbers with the cars made in Vegas.
They began the new series of third-party cars with CSX4750 and counted up from there ever since.
Probably, now, only alum cars and/or special builds will continue with the lower numbers. We are guessing what they will do when they get to CSX4999 with the outsourced cars.
