There are at least four things going on here. And this is the problem with psychology as a field of knowledge.
1. There is no way of knowing how well the tests work. Statistics don't prove anything they are just a tool for searching out possibilities.
2. There is no guarantee that the words people use to describe themselves are being understood and applied objectively when they are describing themselves. One of the big problems with MBTI is that they tend to over describe types with no clear classification of the significance of each item. What is the one thing that makes an INFP an INFP. What is the second most important thing about an INFP etc.
3. There is also the problem of malleability or plasticity of human behavior. Depending on the particular decisions that are made, attractiveness, addictive tendencies a wide range of changes can be made that feel comfortable over time. Identical twins share around half their personality traits - what explains the other half? So adaptability is no small factor.
4. Finally, there are some serious problems with certain psychological theories.
Research has correlated somatotype with certain personality traits that are similar to the traditional temperament categories. The correlations have varied from 60% to 80%. Somatotype considers the fact that humans differ in the constitution of their body and because somatotype deals with fairly large functions of an organism these functions can be expected to influence behavior. My blog on this site deals with some of these issues.
I've somatotyped a lot of people. Those whose somatotype match their type (whether through a test or introspection) merely acknowledge the fit and you don't usually hear from them again. I haven't kept track, and I should and will at some point, but it seems as if the older the subject the more they get the connection between somatotype and their personality. The younger subjects are still in the ego-forming process of fitting in with their world and seem to be at odds with my assessments. Or it could be that older people just don't give a damn.
Let's look at what psycho-dynamic therapy tries to do. Isn't the purpose of therapy to get in touch with your core "self"? Instead of discovering one's SELF the patient attempts to build up a self-concept. Some of the common terms for the self-concept are; persona, ego-ideal, self-system, reaction formation. This self-concept is often the exact opposite of the actuality. What does it mean to lose touch with oneself? What is the natural self. You can puke up endless dreams and analyze the chunks for years and still not know your true self. You can take every psychology test available and be blind to your true self.
So, why should it even bother a person if I come along with a "theory" that says you aren't what you think you are? Isn't it possible that you aren't what you think you are?
But, if you are happy the way you are - so be it - your quest is over. Enjoy your life. Find your love and find your calling and be so busy at it that you can fall asleep and have dreams of total bliss.