I believe my booster (1968 280sl) is original, the (faded but intact) yellow paint daubs are still in place on the mounting studs.
On my booster a larger ATE sticker is at about 3 o'clock on the front face of the booster. It is oriented vertcally and readable by someone standing at the left side of the car. This would be about between the brake fluid reservoir and the washer fluid reservoir, referring to your last picture. If no one comes up with better information, I will try to take a picture tommorow
Gus