Found this Optimus 200 recently. Pretty good condition. Between a collector friend and myself we have determined it to be around 1950’s? It has the older style vaporizer, the square wings on the fuel cap is longer than later models. It also has the fuel level gauge which I believe was introduced post-1938. I saw Nils mention that the black vent cap was the last of the “old design”. Is the date estimate of 1950’s correct?