Most people with BPD that I know (and I know many) do not have narcissistic traits, like at all, like bothingg compared with neurotypicals, who tend to openly display and value their narcissistic aspects. Honestly, "BPD" is a lazy umbrella term at best that is way way overdiagnosed. BPD's who are quiet doormats who cry too much and have no self-worth are sooooo completely different than volitile BPD's who have violent rage fits and are vindictive. It's justified as being the same diagnosis by the quiet ones being "in-acting"(internalizing - "freeze" and/or "fawn" danger/panic response) and the not-quiet ones being "out-acting"(externalizing - "fight" danger/panic response).

BPD's trademark trait is not having a sense of self. Could not be more fundamentally opposite from NPD. Co-morbidities do certainly occur, but BPD's with NPD traits certainly do not represent all/most diagnosed BPD's.