Oh, Wolfgang how I fancy a doubting Thomas. Your are correct that we are just 3 screws from the truth. I am also pretty confident that the proof facility didn't differentiate between O/Us with and without wooden side panels so I feel safe that there will be a regiment of marks nestled on each side of the left centre rib. Now I have seen some Austrian O/U offerings that wear the marks on the right side of the top tube & underside of the lower tubes.
Geyger O/U and note the Sl touchmark on the tubes.
Kind Regards,
Raimey
rse
