I've been MBTIing since 2008...
And now finally I've settled back on ENTP because I gave up and accepted that I probably suck at typing myself. I've been every N-type except INTJ/INTP. Seriously. I think I could convince myself of any type given enough boredom with my current type.
It's now my opinion that THE BEST and easiest way to type yourself is to ask a few people who know you very well to take the online test as if they were you. Triangulate the results with a reading of the profiles, and finally if a close family member that has studied psych hasn't swayed her opinion of your type in 5 years she's probably right. That and more than one girl that I've dated has guessed ENTP whenever we talked about MBTI ...
So in conclusion I think the real problem isn't knowledge about MBTI, but about real self knowledge...