I’ve only seen a couple of people in my career with true narcissistic personality disorder. And I think it’s only because they came to me for a chronic medical problem, not to gain insight into other issues. People with NPD don’t go to therapy because there’s nothing to fix, in their minds. Therapy is generally contraindicated for NPD because they use it to air grievances about how others have wronged them. It becomes apparent very quickly when you have someone with NPD sitting across from you. And they will quickly fire you if you don’t go along with their greatness.
After declaring he was done with treatment after maybe 4 visits, one guy I saw gave me a jar of mustard. I clearly still think about that from time to time 15 years later.