It seems like at least some doctors think bipolar as soon as a patient has mood swings. Either mood swings up and down, or having depression with aggression and/or anxiety. Other doctors seem to think you can actually have some type of hyper mood without being bipolar, as part of another disorder. Some doctors see a hyper episode as the litmus test for bipolar indeed and once you had one you are bipolar forever.

I have met several people first diagnosed with BP and then it was scratched for PTSD. Also I've seen inheriting a bipolar diagnosis, the mother had mania, and one child had depression and addiction, the other one had severe ADHD, both children got diagnosed with BP, because it runs in families, they had issues so it must be bipolar. All these were in USA but that really tells you little since many of my friends are from there.

But still, here BP is often the end diagnosis and not one that can get changed for another. In USA it seems possible to be believed to have BP and then they find out you have something else. Here they rather misdiagnose you a few times before you get the final diagnosis of BP. It is common they think you have BPD or depression before.

I do not know a single person IRL here that has a diagnosis of bipolar. Maybe just by chance but it strikes me as a little odd.

I really can't find any statistics how many people are diagnosed bipolar in different countries. That would have helped. Here it is "assumed" about 2 % have bipolar but I can't even find if those are diagnosed cases or how many they believe have it in all.