Well, you know, you're wrong about one.
My type's been obvious to me since right about Christmas '08... Everything about Socionics clicked suddenly--whereas before it was all somewhat nebulous.
I write this, you know, just so you take it into account...
If the choice is between Fe-IEI and Ni-EIE... In another thread, someone posted a video of the actor named Robt Pattinson... A clear Fe-IEI... Compare with, for example, Dennis Hopper or John Lennon... clear Ni-EIEs.
It can be tough to tell these two types apart, you know?
(I don't know shit about the enneagram. Frankly, I think it's bullshit, a lot of it... But you know, maybe there's something to the 3-4 stuff... 3w4 is pretty clear for me, as far as that system is concerned... You are 4w3?)
The EJ-IP difference can be small re: EIE-IEI... (See Lennon-Tupac comparison in another thread.) This makes it all the harder to tell the difference in some cases.
I agree with you that dating history can tell a lot...That's partly what helped me to get my type right. E.g. It finally hit me that there's no way that the SLE is my dual, as much as I enjoy their company. (SLE is my Mom's type--an activity relation if ever there was one...) Whereas my relationships with LSIs were life-altering.