NY Bach Rotor Stamp Question

[PVH]

I have an old NY Bach 36b with a number stamped on the outside of the rotor valve between the two ports that go into the valve tubing. Does anyone know what a number there would signify?

Thanks!

[hornbuilder]

It is a batch number. The rotor and casing "should" have the same number. There is no record, that I'm aware of, that ties that number to any date. It is purely to keep the casing and rotor as a pair.