Analysis of information sources in references of the Wikipedia article "Polish Enigma double" in English language version.
On the last Saturday in January 1929 an alert customs officer working in Warsaw had been about to process a heavy box when his suspicions were aroused by a request from the German Embassy. Apparently the box had been sent to Poland by mistake and a German Embassy official was requesting that it should be returned to Germany immediately. When the box was opened, an Enigma machine was found inside. The Polish General Staff's Cipher Bureau quickly called in two engineers to examine it.. This date is one year later than Rejewski's date. This reference also has the Polish Cipher Bureau receiving technical details of the Enigma from the French in December 1931 and September 1932.