True, and this brings up another thing. Willow bark is highly regional.
So people were likely to be limited to some degree, in what choices they had. And the winter was isolating for many, I recall reading newspapers from the late 1800s (eg, 1880 onward), about how small towns were so happy to "dig the road out" and talk of "getting fresh supplies".
Even with trains, and shipping, and world wide trade that the British Empire afforded at that time, if your road had 15 feet of snow on it, well.. you weren't going 50 miles to the next town.
So they had to store, locally, everything for the winter. And my point is, 19th century trade was immense.
I can imagine tribes had some trade, but I doubt it happened at most times of the year, and I imagine it wasn't guaranteed delivery of some items.
So I think, truly, local was it.