I was into the Musclecar scene here in Kingston, Ontario back in the late 60's and early 70's. The two I bought new, 69 RS/SS L48 Auto and 70 Chevelle SS L34 Auto, obviously did not come with smog. However, I knew guys that did order or buy 1969 cars with smog setups (Z/28's and L78 Chevelles) and they had the smog setups. I also know our local Chevy dealer did numerous requests from purchasers to remove the setups upon delivery.
I am not aware of this dealer, or any other dealers, removing them on their own before a sale. Obviously it could have happened outside my knowledge area.