I talked with my pdoc about this earlier in the week. He said there were 2 groups of people misdiagnosed as BP: people sensitive to antidepressants who have mania associated with their ADs and BPD people misdiagnosed as BP (often because its more palatable a diagnosis).

There are certainly more people diagnosed since they broadened the diagnosis to include BP 2 and there will be more if you include soft bipolar or BP spectrum disorders.

I have BP 2 and was misdiagnosed as MDD for 7 years back before BP was common.