You have a well-defined test, {SUM(—-(A1:A1999<A2:2000)}, but it is unreadable and does not reference a well-defined unit of logic that is being tested.

The unreadability of the test and the lack of a referenceable unit of logic are directly related. What kind of variable name is A1:A1999? What on earth is the significance of row 1999? I don't even need to elaborate on the inadvisability of the hardcoded "1999." What is column A? A programmer would be ashamed to use a variable named "A" even for a temporary or scientific variable. Is it something so unimportant that it does even bother being named? And yet it could refer to a column concerning millions, billions or even trillions of dollars and critical decisions real world decisions being made on the basis of this comically unreadable code.

I am not being critical of your suggestion, I am being critical of Excel itself.