To be fair, I think any N profile test should also contain a self-evaluation for co-dependency.

I have been thinking about the earlier question in this thread about why we stay or continue to choose relationships with people who act this way. There is the obvious that people who have NPD/BPD, etc. are expert manipulators and suppressors/liars. However, in the light of knowledge, enough clues get through the cracks in their defense that it is OBVIOUS to us in hindsight what has been going on for so long. The clues are there, we just aren't aware of them at first.
I think there are two reasons why WE didn't see see these problems with our N's/B's earlier. The first is that we weren't looking for them. It has been discussed on other threads here how society and relationships operate from an assumption of honesty. That is why lying is so effective. If we haven't been taught or had to learn that some people lie regularly and don't seem to suffer any conscience about it, then we don't look for it because we are not aware that it is a common possibility. Once learned, it is a lot harder to suppress awareness of these problems in others, though it can still be done.

Suppressing is more difficult long term than not being aware of it at all in the first place.
The second reason is that we may actually be seeking people who act this way, even if it is unconsciously. This has also been discussed here in other threads. We seem to have a drive to repeat situations from the past to "solve" them or find ways to fix them. If nothing else, this behavior may seem so "normal" that it doesn't raise any red flags to us. If that is how you were treated growing up, or you never learned to value or stand up for yourself, you may tolerate this behavior because you don't expect any better. Hope for better maybe, but not really expect or demand better treatment.
To really escape from the cycle of getting involved with people who treat us badly, it seems like we need both pieces. As others have posted, it is not enough to be able to recognize an N if the unconscious drive to be around them keeps us unaware of it to try to work out those childhood issues. That can actually lead to serial N relationships. It takes both pieces working together to really break this unhealthy cycle. So, it seems to me that the damage done to us by our caretakers when we were young was the failure to teach us to take care of ourselves, both by spotting unhealthy people and by expecting and insisting on good treatment from others. In some cases, people were actually taught that they DIDN'T deserve good treatment from others or that EVERYONE acts this way, so there is no use looking for anything else.
This to me is the core of the damage that was done. It was not the neglect, harsh words, physical abuse, emotional abuse, or sexual abuse. Those things hurt, but were "only" the symptoms. The REAL betrayal came in not teaching us to expect good treatment and to be unaware that not everyone we meet would be able to treat us well. Parenting that did not lead to us learning to insist on good relationships and spotting bad ones was flawed. It doesn't matter as much how far over that line the abuse or neglect was. It could be an inch or 1000 miles over.
The good news is that whether is was an inch or 1000 miles over the line, there are just two things to learn to heal that damage. I am not minimizing the hurt, pain and the hard work of facing all the abuses from the past and moving through them. That certainly may be worse for someone 1000 miles over the line than for the inchers (like me). It also may be harder to see the line if you are 1000 miles away than only an inch. Stepping back over the line into what we TRULY deserve is the same in both cases. It is the journey to that point that is different. I think that is why we can all share our experiences here and have it feel so relevant, even when our background differ so much. It is the same journey, different paths. I'm not sure if this is profound, but if feels that way to me.