Do they still use red shift for these laser calculations?
Intuitively, I wouldn’t think they would strictly need the redshift of the merging black holes in order to determine that a merger did indeed take place - somewhere. All they need for that, is the observation that the two parts of the split wave are no longer in phase. But you know these guys as well as I do... At a minimum, they’re going to want to know where this merger took place. Did it happen a billion light years from here, or five billion? And for that, they’ll want to know the redshift, in my humble, non-physicist opinion!