I noticed the key advance as well Charles, it does make you take a second look. however it has to be a 1938 model as thats when they introduced the angled body. the previous model had a rounded body, they reverted back to this same body (rounded) post war (about 1948 i think from memory).
i would say the key advance is just using old stock or they were cheaper to buy for a run of cameras they made (i dont think franka made these key advance knobs-i beleive they bought them off of others, and by this time most makers had changed to nicer looking knobs). i have also noticed these key avance knobs used on later year Franka cameras, so i wouldnt use that establishing a year when it come to Franka...for example even the 1936 model often has a milled round knob and not the key advance as well