Bones, About that last letter in Dear Abby, I would tell. I am now dealing with narcissistic in-laws of my son, and it would be an extreme relief if the affected people had a diagnosis and if other members of their family understood what was going on. The main way to keep a narcissist in check is for everybody else to communicate.
Of course, I think there is likely something out-of-whack with the young man mentioned in the letter too, that he is involved with a young woman already diagnosed with NPD at age 20. Which means that the parents of the young woman should be prepared that the news they bring to him and his family might not be received warmly. They might get jumped on. But I still would tell.
For those of you that have been involved with someone with NPD, I am not implying that everybody that gets involved with a narcissist has problems of their own. I just mean that if you are attracted to a narcissist, your own parents are more likely to have been narcissists ... and so, the family of this young man might have similar problems to the girlfriend.
I find it curious that the writer of the letter is the parent of a young woman who has already been diagnosed with NPD at age 20. I wish I could know more about the writer, as well as what their parenting techniques/practices were. If the parents are not Ns, I wonder what factored into this young woman being so N that she already has a diagnosis. My observation is that very few Ns ever get a diagnosis because they don't think there's anything wrong with them, they are perfectly happy as long as the world revolves around them, and those in distress are those in relationship with them.
I have seen articles suggesting that NPD is exploding among the younger generation --- and unfortunately my generation has to shoulder a lot of the blame. My generation seemed to think that setting reasonable limits on their children was unreasonable, and that giving their kids everything without the kids having to work for anything or even WAIT for it was being a good parent.
So, maybe even if neither parent is an N, mistaken ideas about what it means to treat your children well could conceivably produce N kids. I guess.