Bogner XTC 101BS?

[JC-TONEQUEST]

I am getting a used Bogner XTC and in the model number it does not have the "B" nor the "S" blacked out. I know the "B" is for British or EL34's but what does the "S" stand for? I used to own one and the "S" was blacked out. By the way the serial sign translates to 237.

 

Thanks!