NPD isn't mere narcissism.
It's a psychopathic personality and most of the times it's just that bizarre and disordered egocentrism and constant self validation need BPDs also have.
It's just affect and hormones going whacky, people. Narcissists are often the chimp pounding it's chest to appear to be bigger and more threatening.
But NPD is a syndrome - it has more symptoms and behaviors specific to it, not just mere "undeserved and/or exagerated self love and sense of importance". NPDs are usually callous, unempathetic, envious, hypercompetitive, often manipulative and compulsive liars, cheaters, con artists, agressive, hypersexual, cognitive issues, neurological and Axis I stuff is often commorbid, etc.. Mere arrogance is not a disease, people. No matter how big.
The whole host of "wizard of Oz" behaviors indicate, in my opinion, that NPDs are not essencially convinced of their superiority - on the contrary, they are just convinced that they deserve it and get infuriated when they don't receive it!
I would call Narcisistic Personality Disorder something else, like "Compensatory Status Personality Disorder", since most of the times the NPD is just working the smoke and mirrors to appear great, or is constantly seeking external validation.