Do you just pick one and stick to it, ignoring the rest?
Not necessarily. I pick whichever one covers the most ground: can cover more people, is more flexible, and can be explained.
For example, I prefer Enneagram over MBTI, because there is a lot in MBTI that gets strongly tied to outward behaviour.
Ex: in MBTI, tardiness is P, timeliness is J. Indecision is P, staunch decisiveness is J. In Enneagram, motivations can instead show themselves in various ways, and it covers more circumstances / situations than MBTI does due to a lot of its traits being more 'innate'. If anything, stress can help reveal Enneagram, whereas MBTI just hits a dead brick wall, and people try explain it away with grip theory, loop theory, shadow theory, etc- all of which cannot be as conclusively traced as Enneagram and at times even contradict each other.
I am simplifying, but that is the gist of it.
Pick and choose the things that make sense to you from different sources, ignoring the rest?
Combine theories and compromise on some things not really matching up?
This is a bit trickier. If you alter it too much, it simply isn't its source material anymore. If you buy a kitchen knife and add serrated blades and decorations and whatever to it, hell melt it down and rebuild it, it might be more effective to you, but it isn't what it was anymore. Maybe it's a butter knife, or combat knife, or whatever now. It won't be used and understood in the same way.
If people are going to do that, at least be clear about that. I think that a lot of contradictions and confusions in typology stem not only from its base material being inconsistent, but people interpreting it their different ways and thinking their understanding to be the most correct.
Originality aside, it simply makes it difficult to discuss. For example, with MBTI. How am I to know that if I talk about the MBTI Judging Axis, that you are actually approaching it from the same POV, with the same understanding? Miscommunications lead to more misunderstandings, and the typological system will end up failing to do what it was supposed to do- which is to help people understand others and themselves. At that point, just give up and put it down. You're in a rabbit hole, MBTI for MBTI's sake.
The source material must be consistent for discussion to happen at all. How are we to type anybody if we cannot even agree on the basic definitions of the dichotomies?
It's a more severe example of this:
I'm really stuck with Jung's theory not matching up with MBTI and the cognitive functions stacks. I understand what they are - theories - meant to be thought of and possibly discussed without finding complete certainty, and they're as flawed as everything else. They're not really meant to be this be all end all your personality explained thing even if some people use them as such. But if I can't build a foundation on something solid, how am I supposed to keep on laying the bricks?
What I do about it is to not lose sight of the point of typology at all. At least for me, it matters less what someone is called, it matters more that we understand the basics of what exactly it is we're looking at.
As with the silly chart I posted above, someone, say some dude named
John, with a 'Structure Neutral, Ingredient Neutral' POV might insist that a hot dog is indeed a sandwich. You might be a structure and ingredient purist who thinks he is a heathen, sandwiches are sandwiches, you wouldn't bring back a hotdog if someone asked for a sandwich, it's just ridiculous.
However, regardless on what you and John call whatever the hell this thing is:
-if you two can agree that it is what
it indeed is- which is a hotdog bun with a sausage in it, drizzled with a condiment of choice, usually mustard- then what does it matter what it is called? You two are referring to the same thing. You two understand the item for what it is.
With people, that is what matters. You might call someone ISFP via the Dichotomies Theory and John could froth in the mouth and insist that they're actually a looping INTJ in grip via Function Theory, but if you two can see and call out the same behaviours and motivations in the person, you have used typology successfully: which is to break down and understand someone's psychology. You are just calling it different things.
A simple way to bridge the gap in this theory disconnect is to simply ask the person to explain what they mean when they say
"But Madison is sooo J!" and what behaviours and motivations make up their decision. Perhaps it's because she is punctual and uses 9000 to-do lists, or perhaps something deeper. If you two agree on the observed motivations and behaviours, you are simply having a translation issue. If not, you're doing MBTI for MBTI's sake and are likely shoving and forcing Madison into the definitions in order to for her to fit.
A rose by any name is a rose. I consider it a waste of time to debate the technicals unless it leads to actual understanding of the subject material (which, in this case, is the theory and the person both).