Absolutely agree Doug.
This totally clarifies the changes to the model that you highlighted in the Aero Heavyweights 36/38 article in the Douglas club magazine this month and also answers the questions.
Frame part number C/17875 would have had the AE prefix and ran from AE 101 through to AE 1101, shared with three engine types for 1936
Frame part number C/18565 would have had the 6/P prefix and ran from 6/P 101, unknown end but approx 6/P 950? Only one engine type for 1937.
Steve