Many social psychological scales measure tendencies, e.g., you are more of this or less of that. But they don't preclude one person from being more of this and more of that, or another person from being less of both. Other scales are situational, e.g., one can be more extroverted in one situation and more introverted in another. Difference is crucial in terms of interpretation. Types and tendencies are two different things, based on two different underlying assumptions.
Difference is also crucial in terms of measurement.
Keirsey and Myers-Briggs give forced choice questions. One has to rank four alternatives or has to choose only one of two options. As a result, those who end up high on NT must end up low on NF, and vice versa. Those who end up high on SJ must end up low on SP, and vice versa. Those who end up high on one philosophical tendency may also end up high on any or all other philosophical tendencies.