One more curiosity: Is the Tribal dropout zero because they are ultra badass conservationists, or is it because they kill everything they catch, thereby leaving nothing to drop?

Dropout occurs, period. Unless one is on the net 60/60/24/7 some fish will drop. Way back when (80s) there were locations where the pinnipeds net fished. They drove fish into the nets and took them out. Even with the netter trying to chase them. I can't imagine in 30 years that seals got dumber.

A gill net has an optimum size of fish it will retain. That is why there are (or should be) sockeye, coho, chum, and chinook nets. A fish that is outside the target range may tangle, snag a tooth, or whatever. Then, die and come un-netted.

Drop-off on rec gear represents all the fish encountered by the gear that did NOT come to hand. There is associated mortality that is not directly appreciated by the angler. Some fish are mortally wounded by the hooking site but subsequently come unbuttoned out of sight. Some are visibly pumping clouds of blood, but throw the hook or break the line. Some may not be mortally wounded by the hook, but are nonetheless mortally stressed out by the fight (think coho that does that signature death roll just before the netshot.... FISH OFF!). These dead fish are accounted for.

Release mortalities are the fish that die post-release as a result of the stress/injury inflicted by the encounter plus the handling after being landed. These dead fish are accounted for.

Pinniped mortality is fish ripped from your hooks during the fight, while netting the fish, or immediately after releasing a fish that now lacks the vigor to swiftly evade a predator. These dead fish are NEVER accounted for.

FF02,
Release mortality is the fraction of fish that are required to be released and subsequently die. For non-tribal commercial fishers with a standard gill net it is typically 56% of released fish. For recreational fishers, it is 10% in fresh water and 14% in marine water. Tribal fishers do not release anything so it does not apply to them. These two numbers have nothing to do with this thread which is about drop out, drop off and pinnipeds.

Recreational anglers also get charged with drop off which is expressed as 5% of the fish you punched. Suppose you lose 50% of your hook-ups and 10% of them die or fail to spawn. Presto, a 5% loss. Your retained fish counts as 1.05 harvested fish. Non-tribal commercial fishers are charged with a net drop out of 2% for coho and 3% for chinook. Harvest is counted as 102% or 103% of the expected fish in the boat. I can easily visualize this as the fish that fall out of a net as it rises from the water to the boat deck. It is unlikely to represent any pinniped harvest which I think would be about ten times this amount. As near as I can determine the tribal harvest model has no drop out for any reason. This significantly understates their harvest mortality and their share of the harvestable fish.
My comments come with the caveat that I have no current or former connection to WDFW. I am simply using my knowledge of arithmetic to examine how things are manipulated in the harvest models. Sometimes it is a leap to say how they got the way they are.

Well thread calmed a bit so to SB question and we all had thoughts. So here is one. Call it what you may hooking / release moralities / drop out and these terms and words have meaning and are woven throughout the model. Then this fact in our terminal area ( all really ) fisheries mortality numbers, you know the total impact of conducting fisheries, are not close to accurate and it is not that it is not known that the error ( and it is sizable ) is present it is rather just accepted by everyone, except SB, as long as seasons move forward. To be honest I doubt that many really would want to know because frankly the disruption in how business is done with seasons would implode.