BDTS NZM GR is one of the Garib Raths to not have SMB in all coaches.
But, Garib Rath coaches are 130 permitted. So, you might be right about addition of coaches from Rajdhani. But, not true for all Garib Raths. Plus, the berth arrangement in a Garib Rath Coach is very unique, different from any other AC Coach. You have a Half-Coupe near the door.