In Chapter 8 Migsy passes a cinema when looking for the professor. There is a poster for a movie 'Trigger Trail'. It is supposed to be 1938 but Trigger Trail wasn't released until 1944.
At the beginning of each chapter, we are told the story is taking place in 1938, but 1939, 1940 and 1941 model automobiles are frequently seen and even used by the principal players on various occasions.