I am trying to date a men's Wittnauer wrist watch. There is no serial number on the movement, only on the case back (inside). The number is #692927. Can't find anything on Google for Wittnauer serial numbers. The dial is marked "Wittnauer" as is the movement. Since Longines bought out Wittnauer in 1936 I'm guessing that this is pre-1936. The movement is 17 jewel and the rectangular case is 10K gold filled. Any thoughts?