I hope it's okay if I respond to this as I'm not a physician and the closest I will be to becoming one is that I take their depositions. (I'm a court reporter).
That said, I found this thread when trying to find information about whether BPD patients are told about their diagnosis. I was married to a man who I am POSITIVE now is BPD. As far as I know he was never told of this, or at least not as of the time I got a TRO and contact ended. I had met with his psychiatrist, told him of a lot of his bizarre and frightening behavior, and in fact the doctor wrote in my records that it was unsafe to live with him. At that point I had never even heard of BPD but just knew his moods were insane, to use a layman's term. So I started researching bipolar online wondering if that was an explanation, and then I came across BPD, and wow, practically everything I read described my ex-husband. It wasn't which characteristics he had but more like which ones he didn't, because everything I read was him to a T. After leaving him I ended up speaking to his ex he was with 12 years who he simply referred to as "the bipolar." Well, she is bipolar, but she's also a nurse in a psychiatric ward. I mentioned to her that I thought he could be BPD and she said she agreed. Also, I sent some info to his sister and she said it sounds like him. I may not be a medical professional, but I would bet any money I make for the rest of my life that my ex has BPD. So his ex tells me she thinks the psychiatrist was scared to tell him he has a personality disorder because he'd flip. She also went to the same psychiatrist for years with him. I only went twice, at his urging, to "fix" me I guess. For the record, I do not have BPD or bipolar, but yet living with him was driving me nuts. One time early in our relationship my ex's mood shifted so crazily I asked him if he could be bipolar and he FLIPPED OUT! He has even been admitted for suicidal behavior overnight and the police had to come to his house and take him to the psych ward. As far as I know, no diagnosis ever of BPD unless it's happened since I left or it's in his records and he doesn't know it, and he's been under psychiatric care and sees a counselor weekly, for years, from what I know.
Now, after I left my husband I started dating a new guy who I began chatting with on Facebook about how my ex had BPD and his mom had BPD, though neither formally diagnosed. I was seeing the new bf long distance but started to notice similar BPD characteristics in him. I'd let them slide, but then more and more moodiness and childish behavior kept happening (he's 34, I'm 41) and it was just too stressful, so I decided to end the relationship. I mentioned to him that he seems to have BPD behaviors, and, like my husband when I said he was acting bipolar, he FLIPPED OUT, saying I'm not a doctor and I can't diagnose him through texts and e-mails. Well, true, I'm not, and told him that, and it's also not my job to listen to him go on and on about how I probably hate him and how miserable his life is, "just the way it should be," have him tell me to "f*** off", etc. He is seeing a therapist and has told me he had to work on his "black-and-white thinking" and has told me he has an intense fear of abandonment. He also was prescribed lamictal but claims he's not bipolar.
Sooooo, there's a lot more to why I'm sure my ex-husband is certainly BPD and see the tendencies in the guy I stopped seeing, and I know I'm not a doctor, but I have lived with this in my marriage and it's pure insanity. The point I'm making is it seems if you tell them that they might have it they get really upset, and that said, they may discontinue treatment thinking you are "against" them. I am in therapy with a very good therapist with a PhD who has been practicing over 20 years. I brought this up with him, asking if he tells people if they have BPD or not. He seemed to say it depends on the situation and sometimes you treat the traits that are problematic. I actually did ask him if I am bipolar or BPD because I started to wonder after dealing with my ex and then the new bf if maybe I'm the crazy one! He said no, definitely not. I guess thinking as a rational person, if someone close to me thought I was BPD, bipolar, or anything else I would wonder why they thought so and examine it if I saw validity to what they were saying, not just take it as some insult, but yet both of these guys acted like I'd just told them they were a total piece of crap, not tried to say they had a psychiatric disorder. But they both would get very irrational, and it was like dealing with a two-year-old throwing a tantrum.
Since my divorce I've been reading a lot about BPD and find it really fascinating. I wish I had the time to go back to grad school and study psychology, but I have a stressful job and bills. I've read that a lot of people don't like treating borderlines and I can see why after living with one. It's like the sense of logic is literally that of a toddler sometimes. My ex-husband is 42 and is very intelligent, but yet when he'd flip into psycho mode it would be like taking care of a child having a tantrum, only a drunk child who carries guns and knives. I literally had to walk him home from a restaurant sobbing once like a little kid holding his hand and pulling him. And that's just one incident. I guess I've lost a lot of patience after living through that. It really wears on you.