If you have no reasonable way of knowing that what you are doing is a crime, then ignorance of the law *should* be an excuse.
Unless the “pot” is IDed as to time and place of collection, how can any “crime” be shown, unless the police have proof of date of purchase. There are numerous fakes out there. Proving authenticity is not a simple consideration.
I suspect the Hillerman has quite a bit of fact in his novels, but they are still fiction. I would not rely on them for legal advice. A lot of this law is pretty murky, I am told. Virtually all writers of fiction are prone to “stretch” points to make a plot better.
Something that I have noticed is that the major publishing houses are *very* politically correct, and go so far as to insist on plot changes to fit their political agenda. If authors do not toe the line, they do not get published.
That is true but read the book and then report.
We are not a court of law. Hillerman did meticulous research and lived in the middle of all the cases. He was a newspaper man.