Having just come in on this interesting thread, I noticed other features on the photographs not yet mentioned. The colour demarcation lines are uneven and rough along the wings, lower fuselage and engine cowling. This strongly suggests to me an undersurface repaint. The serial is still visible on the rudder which suggests no change in the upper surface colours; ESG /DSG were not a scheme in 1939. The dark area under the leading edge might be black, it is difficult to be sure with the reflections off adjacent the top surface.