I have got a Zeiss Ikon folder in absoute mint condition (stunning, like new) and i am trying to find out its age. The model is Nettar 515/16, it has a Nettar-Anastigmat 1:6,3 F=7,5cm lens in a ACG Telma shutter with shutterspeeds from 1/25 to 1/125 plus T and B. There is also a serial number, K 318 on the side of the back that do not lead me anywhere.

The model and the lens/shutter combination seem to be a bit conflicting, the lens/shutter suggest it is quite a bit older than what i have found about the model.