The single largest export of the American colonies from pre-revolutionary times well into the 19th century was hardwood. As early as the 1690s America was identified as a major source.
There was plenty of curly maple in Europe. They used it for violins since the 1500’s.
These two valuable insights illustrate how certain assumptions make the attribution business (one could call it other things) extremely conservative. If you assume that curly maple indicates American-made, then firearms made of curly maple will be routinely attributed to American makers (or at least identified as American made)--swiftly the pool or corpus of American-made curly maple firearms will grow larger and larger--and it soon becomes more and more unlikely that any firearm made of curly maple will be attributed to anywhere other than America--it's just too "obvious" that it belongs with these others.
All attribution categories work this way (i.e., they are conservative and self-confirming). The one that interests me most are the "schools" that Kindig introduced.
Once we conclude that the "Roman nose" comb is characteristic of the Reading school, then any rifle (maker unknown) with a "Roman nose" comb will be assigned to the Reading school. But that just eliminates (through attribution) what may actually be significant variety. Maybe that rifle with a "Roman nose" comb was produced in Lancaster or Lehigh county? Maybe some maker in Lehigh or Lancaster imitated somebody in Reading? Or maybe the "Roman nose" was, without much thought, produced in all these places? The conservativeness of the attribution business obscures this--because each new "Roman nose" rifle will be inevitably placed in the "Reading school" and so more and more "Reading school" rifles will have the "Roman nose" and ... well, it becomes less and less likely that any "Roman nose" rifle would be attributed anywhere else.
So, maybe, with regard to curly maple, we simply cannot use it as an indicator of whether a firearm was made in America or in Europe? Sure, that leaves things uncertain. But why do we need to be certain about something about which certainty is really not possible?