The problem with the way in which we test using MBTI is that it doesn't quite work when connecting your 'letters' to your actual type. Consider the following scenario:
You are an ISFx. You normally score as ISFP, but recently, J has become more evident. So what does this mean, you suddenly go from having Fi and Se to having Si and Fe as dominant and auxiliary functions respectively? It means your whole psychological makeup changes, just because of the way in which you're scoring? Of course not. This is why, as Splittet often professes, typing by functions is far more effective. It makes much more sense, and is so much more logically consistent.