Krugman is a joke. Usually, in science, if the data don’t agree with your theory, your theory is wrong and needs to be changed or discarded. For Krugman, it means that the data are wrong and need to be ignored.
Of course, that’s how one has to approach things if one is intent on being a Keynesian.
You sound like you learned science a long time ago.
Nowadays, so-called scientists—even in “hard” science—start out with a theory and then stack the deck to “prove” it. Once upon a time, that would get you a failing grade, even as an undergraduate.
Krugman merits a big, fat “F”-—naw, make it a ZERO-—in the area of scientific method.