stradivarius

I'm talking about the C trumpet bells. What is the difference in sound and physical shape between the 229 and 239 bell sizes?

with the bell. Can somebody help me? The serial number is ML 0999, but this serial number dates to the late 20s, and the bell on the trumpet, a model 43, was made in Elkhart, IN., and Bach didn't move there until 1965. Clearly something's amiss, but I can't tell if the serial number is fake, or...