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I grew in in Michigan so I've been trying to read up more on the history of York tubas, mostly from their Wikipedia page. I'm a relative newbie on this so please forgive and ignorance. I'm trying to understand which York tubas were made in Grand Rapids versus which instruments were made eventually in Europe. So a few quick questions:
1) What are the differences between a York tuba and a York Master tuba? Does being a York Master mean it was made in Europe later on?
2) Before 1940, were all York tubas made in Grand Rapids Michigan?

The 'York Master' tubas were made by Bohm-Meinl (later Nirschl) in Germany. They were what I'd call 'York inspired' tubas.

The original York tubas were made in Grand Rapids, Mich. 'Grand Rapids Band Instruments' were York stencil instruments.

Yes, I believe all early pre-1940 Yorks were made in Grand Rapids.