Assuming constant interceptions, even back then, was wrong from a biological sense but "worked" from an allocation and even conservation.
Escapement should be measured independently so removals by predators (pre spawn) has no effect on the escapement estimate. There are enough problems with how they do escapements anyway, but that's another whole thread.
Net dropout and release mortality should be included. They should be more or less real and not just "agreed-to".
Seals have increased and have learned to fish. In the 80s there were some I knew of in Dungeness Bay that actively fished gillnets.
IF achievement of the escapement target is the primary goal then fished planning starts with a run size, subtracts ALL mortalities, and when the harvestable number is accounted for the fishery is closed. We used to have net dropout as a number. That came off harvest. It can be done, but the short term would mean reductions in fisheries.
Just ask Rivrfshr what would happen to some gill net fisheries if the actual release mortality was accounted for as it occurred.