Yes, each barrel "tube" has a number, usualy in couplets. I'm not sure of the exact manufacturing process, but is my theory that it was a way to keep pairs of chopper lump barrels together. It does not seem to be a patent use number, as the early Whitworth barrels don't have either tube numbers or the "wheat" logo; and the tube numbers continue long after any patent was still in effect.
All the best, Mal