[Someone]

There also is (FTA):

“I took the countless papers that start with the standard return estimates and tweak them with one novel complication. Then I merged all the tweaks that seemed convincing to me* to get final policy-relevant numbers”

So, the model was adjusted from tweaks created by one person, and then those tweaks were evaluated by the same person, not on objective criteria, but on what seemed right.

I also guess the author at the start had ideas about the quality of each of the “countless papers that start with the standard return estimates” and used them to pick those he included in the model.

I don’t see how that could ever lead to an objective model, even if the author started this exercise unbiased.