Jeez, it's been so long since I've dealt with most symptoms that I'm struggling to even remember. Actually, I don't even have much interest in talking about this stuff anymore, either...I just realized because I don't feel like trying to remember, not interested in delving into all of that. Damn, I'm a bit taken back by that, as it is a stark contrast in comparison to the way I was the last time I frequented this forum. It's hard to focus on other things besides your broken arm when your arm is broken and hurts like hell, though. My arm is no longer broken, so to speak, so I don't focus on it I guess. Anyway, I'll force myself, since I've already written this much anyway.
I realize this is slightly different than what is being asked, but most of the distinguishing I have to do has pertained to root causes. For instance: the fear of loss...is it from borderline, PTSD, or from injury left by narcissistic abuse? The extreme mood fluctuations...are they from borderline, or from rapid cycling bipolar? Basically, having to pinpoint the origin of something that multiple diagnoses share in common.
I definitely mixed things up initially, as did the psychiatrist who misdiagnosed me with borderline (they didn't know my past history, which involved 20-something years of narcissistic abuse). I remember an embarrassing phase in which I actually tried to identify bipolar mood swings VS borderline mood swings when they happened, even, lol. I suppose things only became more distinctive while overcoming the entailed challenges over time.
My load lightened enormously due to getting the right medications in my system, which is when I started to notice the fact that I wasn't having mood swings anymore. It wasn't that I learned self-control, which I needed tremendous amounts of before I was on meds; it was that there wasn't actually much of anything even there to be controlled. This is so much the case that, in the rare event that I do have to live without medications for a while, I am no longer as good at coping as I was before. It's like lifting more weight than you're used to, it requires some adjustment. I'm out of practice with coping with anything that intense. That was among the first indicators, to me, that my borderline diagnosis was a mistake. This is because medications do not correct the mood swings of borderline, they only work for bipolar. What one therapist explained about how bipolar works also helped. She said that when feelings are triggered, the brain chemicals can basically just get carried away and go too far into the extremes, unable to maintain appropriate levels. So, I guess, the short version is...the way I was able to tell the difference between the origin points of the mood swings was through knowledge about the subtle differences in the disorders, and with trial and error (finding that medications corrected things; if they hadn't, it'd have told me that it likely wasn't bipolar).
I'm at a point now where I have MAYBE 2 out of 9 symptoms of borderline personality disorder, but I know the exact reasons why I have those things, I know they are caused by specific traumatic injuries/the way things in my life are structured, and I know exactly how to overcome them. I'm just still in the process of working on them, as Rome wasn't built in a day. The vast majority of those symptoms that I already overcame really boiled down to narcissistic abuse. I had no idea there was so much similarity between damages in narc victims and borderline, so again, it really boils down to being educated about the different nuances of psychological matters. Sorry, I don't feel like explaining in more detail than that.
EDIT:
Well, I will if anyone asks me to. If it could potentially be helpful to anyone, I don't want to just say "no cuz I don't feel like it," that's fucked up...so feel free to ask if it would help.