The two are combined because that is the point of the story, comparing and contrasting. My sources are in the article (underlined), though I have referenced Sam Vaknin before, I'm not a fan, he's become a bit too 'pop psychology' of late. I mostly use references from recent psychiatric and psychological journals, previous clients, and I use my psychology text books rarely as I do prefer to keep up with the latest research. I am interested that you state NPD's target BPD's rather than BPD's attract NPD's. I guess that's seeing the same thing from another angle. Story for another day maybe:)