Not only is it basically impossible to fully calibrate one socionist's typings with another's, but an isolated socionist's clarity about types and relationships is fully capable of eroding by itself. This post illustrates how that happens.
In recent years my view of the central importance of socionic factors (types and intertype relations) in personality and relationships has been steadily eroding under the weight of life experience. The graphic below illustrates this process. Many readers will probably be able to recognize their own position somewhere along this timeline:
An example of how this happens is having experience with more than one intimate dual relationship that seemed to have a very different "energy" to them due to considerable temperamental or other differences between the people of the same type.
An experience like this can lead one to begin looking at relationships through a different lens, which, in turn, can lead to a reevaluation of other relationships as well. Other relationships belonging to a single intertype relation which previously appeared more or less similar "in essence" may suddenly appear to be more divergent than before.
This goes back to the idea that as one studies a subject and begins to think in new categories, one mentally puts things together in new groupings, bringing some phenomena closer together and others further apart — in one's mind. Later, as the subject of study loses its influence on mental processes, the person may find that previously grouped phenomena are drifting apart in his mind and that there is no longer any compelling reason to place them together in the same category. That is the process I've described here.
As the overlap shrinks from explaining a hefty share of personality or interaction to being a kind of "hidden essence" that requires increasing perceptiveness and training to perceive, eventually you have to ask: at what point is the commonality too small to be worth making a big deal about?