the thing about the jcf theory is that type is something that is only malleable within its own box. so your type doesn't actually fluctuate, it doesn't change, you just grow into using all of your cognitive functions maturely.
you can't score middle of the road on something (which is where meyers-briggs has led most people to assume) and you especially can't get something like “INTX” or “INFX” because the judging function is the one that decides the orientation of the rest of your cognitive functions.
i.e. an INTJ vs an INTP is ni-te-fi-se or ti-ne-si-fe, ne and ni are completely separate cognitive functions, one is extroverted and one is introverted. so, one looks for meaning externally and one looks for meaning internally. so are fi and fe- which are basically antithetical. fi is an internal values system while fe is an external values system. te and ti opposing too, te is an external, practical function while ti is an internal examining function.
so you see, you can't have both, because you can't, according to the theory, process information in both ways or you wouldn't be able to sort it out.
another interesting part to the jcf side of things is that some people (especially people who aren't mentally healthy) fall into primary-tertiary function loops so you might get an intj who goes ni-fi instead of ni-te, which would cause problems because internal searches for meaning would only reference internal emotional value states, causing loads of irrational paranoia and chasing in circles.
some types that don't look very similar actually can be. for example infps and estjs have the same functions, just in reverse order (fi-ne-si-te vs te-si-ne-fi), so do istps and infjs (ti-se-ni-fe vs ni-fe-ti-se) etc. so if you notice you relate with certain cognitive profiles that don't fit your understanding of your established personality type, you may be using your cognitive functions within a separate framework than you think, or you could be in a cognitive function loop.