I think it does all come down to honesty, and there is nothing wrong with that. I believe if someone is selling something as specific as big hill river roads, it only makes sense that they can prove it back to the original snakes from the big hill. If they cannot be traced back to the originals, the term big hill is still subject to interpretation, and I would not recommend you breed and sell the babies as "Big Hill".
If you have, say "river road locality" snakes based on someones word only that is fine by me too. I have seen generic snakes labeled "River road type" and that is quite misleading wether intentional or not.
I have an example of loma alta area snake I have owned for about 7 years, I bought a female Gas station locality female and raised her up, she produced a nice group of offspring this year, and after digging into it I was able to get pictures of her f1 parents which were produced from wild caught parents one was found at the gas station and one was actually just to the south a mile or two. Personally I would have called them 277 or loma alta alterna, not specifically "gas station", but because everyone in was honest about it, I am glad to have better and accurate info and a nice locality snake also.
It is always good to not go more specific about locality than you can verify 100%, Honesty is most important, but also keep in mind that memories fade, and details blur with time (for some people)and peoples various opinions and communication abilities also factor in.
Jim