What you are seeing in regard to pricing is simply the economic market at work.
The first catch of true Copper River always sells at a premium to those that just must have it at any cost. Later catches sell for less as the demand slows but I suspect that there is actually much more 'Copper River' salmon sold than is ever actually caught and that 'Copper River' has become like Atlantic Salmon, purely an adjective with no legal or informational significance.
Sockeye is certainly easy to distinguish from other salmon and i have found even Sockeye being sold as river specific. My fish monger at Grash's in Milwaukee who does a good job of ordering and knowing the source and pedigree of his fish, had Copper River, regular King Salmon, Sockeye and a River specific Sockeye, yesterday. The pricing was all over the map and depended on who was selling and at what time. A sockeye that sold for about $11/# yesterday would be $14/# with the next shipment due today.
Me, I purchase by quality and freshness and ignore the appellations which usually result in either higher prices or generic catch anyway.-Dick