One thing I've noticed is that the 1939 cars (red car with no numbers on it, listed as "street version", and silver car #6) do not have the stripes above the headlamps, and the 1940 cars do. Check out the attached:
http://www.alfamodel43.com/Alfa%20Ro...ssa%201939.htm
I'm still not sure if there were 2 or 3 cars with Ala Spessa coachwork....