I think you captured it, kinda, as to Coho but the sharing impacts are what resulted in the one bag limit and 2 week shut down window. The Nation gets 50% of Grays Harbor Coho ( it is the aggregate of Chehalis and Hump ) and the Chehalis Tribe and ocean catch count into the states side. The two bag limit from Sept 16 to Dec 1 is regarded as a full Rec season bay or inriver. Species are removed from the bag limit by returns limiting a species availability, sharing, or GHMP on the states side. Chum after the modeled harvest had 3020 left in the states side. That means the two fish bag should have stayed with zero Chinook retention and only one Coho in the bag. After all that 3294 Natural Coho and 21814 hatchery adults left unharvested. The hatchery number means almost nothing as the fish are managed to the wild escapement.

The main words here are 50% entering WA ST waters and aggregate Hump / Chehalis. PFMC and the nation manage to the Grays Harbor aggregate. So when you do that the Grays Harbor natural Coho return is 34,146 and the escapement goal is 35,400. It is the Hump Coho that pull the total down as the natural will be 4549 under Grays Harbor aggregate escapement.