On this one I have thought about this a LOT and I've done some research. It seems to me that generally, it's acknowledged that NPD (or NPD traits) are generally considered to often happen as a result of childhood trauma and/or the child's brain not developing correctly due to poor parenting, outside events etc. Certainly, when I consider that almost every child I've ever met appears to be quite narcissistic, that makes sense - they have to LEARN not to be this way, and if they don't learn it, they carry these behaviours over into adulthood. On that basis, I think it's entirely reasonable to assume there's a lot of overlap between people who are ND and those who are more likely to develop NPD because by definition, those ND people are more likely to experience trauma or poor parenting, or struggle to learn certain lessons.
I think the thing about narcissists, particularly covert narcissists, is that they are completely unaware that they are the problem. If you consider that other personality disorders are generally often believed to at least be somewhat conscious that their reactions, emotions, behaviours are different to the norm, the very nature of narcissism means that narcissists cannot see that. They believe THEY are the norm and that everyone else is behaving oddly.
In the case of the very clear Covert Narcissist in our lives, I have had to find a place to reconcile the cognitive dissonance of hating him with every fibre of my being, while simultaneously feeling extreme pity for him. I believe he was hugely let down by his family, and then by the state and education systems and that has led to where he is today. I suspect he absolutely does have some ND as well, which of course was never spotted because of the issues he was experiencing as a child. Feeling those two things simultaneously is a very strange feeling.
@ItReallyDoesntMatterAnymore I don't know anything about your H so I can't say, but I think lots of Covert Narcissists are genuinely unhappy, which is why I feel sorry for them too, and their "empathy" is not really empathy in the way we think of it. I believe that they do feel sorry for that person who has had something terrible happen to them, for example. But it's still ultimately about them - and how bad it makes THEM feel - if that makes sense at all?