Might it be possible that a a misdiagnosis on bipolar disorder occur even after numerous tests and doctors?

Yes: Disorders like depression, substance abuse, personality disorder, adhd, intermittent explosive disorder (and others) can be mistaken for bipolar disorder.

Absolutely: Tragically, is not uncommon for a person suffering from bipolar disorder to have been symptomatic for more than a decade, seen multiple clinicians, and carried several different diagnoses before he or she is correctly diagnosed and treated.