Could be. There is practically no difference between a D31 and a D32. For that matter it could be a 1930 S6; other than the cosmetic difference of the tartan panels were introduced in 1931. You would have to make a estimate based on how high (or low) the serial numbers were. Likewise it could be a 500cc (S5 or C31). In 1932 the 500cc side valve (C32, Bulldog model) became based on the 350cc crankcases with bigger cylinders, rather than the 600cc with smaller cylinders. So not one of those.
-Doug
