I think it is hard to get an independent evaluation once a person has a diagnosis of bipolar disorder because, unless you happen to show up for the evaluation in a manic or hypomanic state, the psychiatrist will not discount previous observations and just assume they have not seen you in all your mood states. According to many psychiatrists, people notoriously under-report manic or hypomanic symptoms so they will not take what you say about those times at face value anyway. At least that is what I have been told and also heard listening to talks on youtube...

I have had more than 10 psychiatrist evaluate me (including hospital admissions) and even still there are times when I don't believe the diagnosis. Sometimes this is because of the social stigma and negative self-evaluations that occur and sometimes it's because i think I have a different disorder like schizoaffective and sometimes it's because all of my psychotic episodes have been associated with long term daily cannabis use that has now ended..

But ask yourself, let's say the 4th psychiatrist also says you have bipolar. What would that change in your mind? Would you still have doubts?

Be cautious about any hallucinations with a possible diagnosis of bipolar. Also if AD don't help with depression (that is true in my case) then that also increases the likelihood that it's bipolar.