Let's simplify this.
201-1 Treadle machine, no matter where it was made.
201-2 Pot motor machine, most were made in the U.S.
201-3 External motor and belt, made in the U.K.
201-4 Natural born hand crank, again made in the U.K.
Now this is just for the older cast iron versions, but we see very few of the others here in the states. The K and the -1 etc weren't on the machines, they just say 201. Even the 1200 version until the last few years of production says 201 on it.
And the chrome spool pin plate? Some have it, some don't. I think it may have been another early 1950s change like the decal and face plate changes.
Cari