The Buffalo Creek cars were pretty common in Minnespta at least thru the mid 70s.  A lot of wheat moved by lake boats from Duluth Superior to Buffalo.  Some years they were not able to get  it all moved via water before freeze up, in those years expect hundreds of BCK boxes to show up in Duluth Superior for wheat loading to Buffalo. I recall solid trainloads of loaded BCK boxes heading east for Chicago mostly via SOO.