It is just a guess on this, but handcrafted vessels with a stopper often have a code under the vessel base and the stopper, which is needed for the packers in the factory, so that they know that both are belonging to each other. The stopper is often refined by carving and polishing to fit exactly into the decanter's body, so that it fits tight without easily getting stuck in there on the other hand. I don't know too much about postwar Daum, but if they hired Designers in the post war period, those were mostly quite celebrated artists, designing small editions that are extensively signed, dated and limited. Your decanter looks more like the "simple" factory designed luxury tableware from the fifties or sixties. Like I wrote before, this is just a guess though.