I absolutely disgree on your point regarding tert/inf expression as people age. It is an immature expression of those functions, unconscious, sloppy, ill-refined, damaging, shadow and erruptive as it emerges, but very present and can create a great deal of issues as they change. Jung noted this as seeing a once young, sweet women morph into the household provider during middle age, while her husband moved from being assertive to being passive. On mbti step II you can actually see the inferior functions bleeding through-in the Ni doms, you see heavy S scores. On the T-F axis, this can play such a large role that they created several designations to capture the effect "rational feelers" and "empathic thinkers" to describe sub-facets that are skewed.
In giving MBTI step IIs to people, I had to make a little powerpoint slide that showed the different functions they had and how they might change over a lifetime depending upon life experiences-then they would accept their MBTI results. Before that the test results and their feelings of themselves were too conflicting on the diacohtomies, and they were very frustrated by what they saw in the results.
In older couples, you see these issues come to the surface as each changes-thus to ignore dynamic changes in personality over a lifetime, would be to create an incomplete theory.