Having worked with actual catch data, but it was back in the 80s, talked to fishermen (rec, commercial, tribal) I was told more than once of catch that was not reported, reported for other areas, and so on. Many of my coworkers had the same sort of stories from other fishers. That doesn't include investigations and documentation by LE.
That said, the only numbers that can be used for management are defensible ones that everybody agrees to. The state and tribes have agreed as to what they will use and how they will collect/develop/collate/estimate. They are what they are.
But I still maintain that if we had accurate (not precise) numbers of catch and escapement that we would be surprised at the actual number of fish out there.
But, just because we are (say) underestimating escapement does not mean the runs are in better shape. PS chum escapement goals were initially set as the mean of the three highest years. Some folks looked into it 20 years later and found that the escapement numbers we were using were about 1/3 of actual. So, these geniuses thought we actually had a lot more fish to catch if we estimated escapement correctly. Nope. If the number we were using was an underestimated number and the real number was 3 times higher, so was the goal.