"In very general terms," says Testie, "an NPA+ type with mental retardation or low intelligence... or with genes predisposing to ADD... or with genes predisposing to temperamental volatility... or with unusual "nurture" ... or with unusual real-life situation ... or with an unusual combination of "usual" genes... or etc., etc. -- or a combination of these -- could give mistaken Test results of NA type. Thus, it is quite possible for an NPA+ type to be mistaken for an NA type".
In cases of disagreement, lacking a genetic test, the best that one can do is to look closely at first-degree family members (parents, siblings, children). But one should not be surprised that sometimes there is disagreement. Even in the case of male vs. female, there are individuals for whom no amount of discussion would resolve the issue whether the individual is male or female. Sometimes a genetic test is necessary.
As to the PA− type, this type has been discussed recently:
In the NPA model, the PA− type is a non-sanguine, introverted schizoid type, or a borderline schizophrenic individual.