This has gotten off-topic, but I'd like to give my 2 cents regarding BP and BPD.

I think that there are symptoms that overlap, but it's a question of context and pervasiveness. If you're experiencing x symptom/behavior and it fluctuates on a daily (or more frequent) basis, then you're more likely to be experiencing BPD. Also if your behavior is, more often than not, a reaction to interpersonal strife. Bipolar Disorder is not pervasive, as PD's are, it is episodic: episodes last for weeks, not hours or days, and although episodes can be triggered by any number of things, everyone is different, it's not necessarily so frequently triggered by interpersonal issues.

That said, I do think you can have both. But this doesn't bely what I believe to be two very different issues.

I do believe it is important to know your diagnoses, if for no other reason then to receive the right, targeted, treatment. It also helps many of us to know why we are experiencing what we are experiencing.

And I'll end with what will probably be an unpopular opinion, which is that I believe CPTSD, whose symptoms hugely overlap with those of BPD, is a form of BPD caused by trauma, especially early trauma. However, there truly are plenty of people with BPD who have not experienced this kind of trauma, and yet suffer from BPD nonetheless. So I think something else is often going on there for those diagnosed with BPD. Personally, I think that they should separate what could be BPD with early trauma, CPTSD, and BPD without early trauma. I expect some of the treatment would be the same (i.e. DBT), but those with early trauma might also require trauma-focused therapy.

Again, just my 2 cents.