^ The key being the generation of a tailored corrective preset specifically matched to the deficiencies of that specific piece of gear (microphone). "Close enough" in this case has to be really close, requiring measurement that is specific to the problem in order to end up with something better rather than worse or just different sounding.
This has one great advantage over speaker correction filters and room correction techniques, both of which are now common, by way of inverting a problem those approaches are unable to escape. With speaker and room correction the test signal is simple and non-dimensional, but one must choose a listening position from which to measure, and the correction will only truly work for that point in space. From other listening positions it can and often will make the perceived problems worse. Yes, there are averaging and windowing techniques used to mitigate that, but the problem is rooted in complex geometry differing on the listening end, making it essentially unavoidable.
We would instead be doing something of the inverse. The correction in our case will always provide the same effect on the output past the microphone. The corollary to the aforementioned problem is the geometry on the opposite, test signal input side. Using this technique, we can't fix or modify the polar behavior of the microphone, only its overall aggregate response with regard to frequency, phase and level. So the question becomes whether to try and target the direct on-axis response, overall diffuse response, or what - the complex geometry on the other side of the microphone. This is where the use of the our standard "program material" (live music in a venue as we would otherwise record it) as test signal is not simply a super convenient way to do this, its a test environment that provides the same or very similar expected balance of direct and indirect sound that the microphones will experience when used in other taper recording situations.
So we don't need to really do much out of the ordinary to setup a good, applicable, and generally repeatable test situation, except to go tape something like we typically would, using the music in that acoustically complex geometric environment as test signal, which is representative of how we will use the microphones anyway.