You have sailed past the point. There were so, so many cod it was hard not to catch a bunch. That isn’t a metric, it’s an indicator that most likely meant vast unseen numbers. The tip of the iceberg is a metaphor for a reason, though it may become an anachronism within our lifetimes.

I think their point is that discounting the time estimates is more a constant shifting of the window of what we expect more than them being de-facto incorrect. They’re more off by degree (e.g. an XX% reduction vs complete extinction) than being worthless. As the example points out a large reduction can be very similar to an annihilation it’s just that we are only used to what we know so we constantly shift what is normal.