One main problem is that NPD is a clinical, subjective diagnosis made by a health care provider. Even in a single country, there is bound to be a spectrum of opinion as to which criteria should be considered most heavily.
The second problem is that to do the study properly, the mental health investigator would have to be skilled in knowledge and experience with the NPA model, and in addition would need to have a vast clinical experience, i.e., with actual psychiatric patients.
So, we are years away from such an individual.
So, here on the Message Board we are limited to speculations based on limited observations...
I would agree that the NP type certainly can become egocentric enough to satisfy most of the criteria that describe NPD. Some of these individuals even get involved in criminal acts that seem always to shock those who knew the individual previously.