50 versus 16 point towards a mismatch between bell and body, as the collar numbers were intended to keep parts together from the assembly through the buffing and finishing processes.
As a former band director I can attest to the following...........If a school has more than one sousaphone, the chance that the bell and body will stay together for 3 or more years is 1 in 56.
I am fortunate to have a great job that feeds my family well, but music feeds my soul.