Yes, no, and maybe. The typical MBTI only reveals to you exactly what you had told it moments before, so it is very accurate. Test results will change, however, because you change over time.
Interesting counterpoint - more than one test-giver has told me that, no, in fact, your 'score' doesn't change. I don't believe that for a moment, because taking the test is rather mood dependent - I've taken MB multiple times, and while overall, I come out similar in some areas (always an I, for example), the T and F have changed on occasion. It make total sense - my view of things changes over time - but these administrators were rather adamant that it doesn't change.
I guess if I'm an INTJ, taking the test the next day, I wouldn't expect to be an ESFP, but... over 10 years, I wouldn't be surprised to see an INTJ get a different 'score'.
