This is just a SWAG, but I'd expect that the lower SN would likely be from the 1928-1929 time period, while the higher SN would likely be from the 1937-1939 time period.
IIRC, there were around 18,000 Model 40 and 45 Super Sporters made, around 12,000 of the 40s and 6,000 of the 45s.
The earlier 40/45 Super Sporters had a rounded "British Style" forearm and the magazine release was a tab on the bottom of the rifle.
The later 40/45 Super Sporters had a schnabled forearm and the magazine release was a button on the right side of the stock, about mid-way between the bottom of the receiver and the bottom of the stock.