First of all, there are 16 distinctly different personalities, i.e. types. That's a fact. Furthermore, SEE and SLE are similar, and LSE and LIE are similar etc. So it is very likely that we have 8 cognitive functions and 4 blocks. (... or 16 functions and 8 blocks in Model B, Model D etc.)

Ti and Se must complement each other. I think Ti evaluates an object's position in space, and Se tracks that object.

Si and Te must also complement each other. I think Si is about identification of an object, and Te determines whether it is identified or not.