MBTI and cognitive functions

When I attempt to type a person, I try to type them according to Myers Briggs and later try to resolve any inconsistencies by checking with cognitive functions. I was wondering if this was a valid way of typing someone.



For example, if I think that someone is a P based on what I observe, does that guarnatee that he is using perceiving function (Ne/Se) ? Is it possible that the person is using Fe (a judging function) while he comes off as a P ?

I try to go by functions. Thing with the profiles is that they are too stereotypical and some people will never quite fit them. Some profiles also confuse mindsets with skillsets. If I know what each function represents, then hear the person talk or observe them do something, then I can match functions to the person's values and narrow down their type.