I can only speak for myself and my particular psychiatrist.

As far as the diagnosis that prints out on paperwork from my psychiatrist's computer, it has been Bipolar 1 with Mixed Episodes for at least 10 or more years. I have definitely not been in a mixed episode for even much of that time. Most of that time I was stable, euphoric hypomanic, or mildly depressed. I have had severe full blown manias, some with mixed features, and depressions, but less often than stability and mild mood episodes. I think my psychiatrist just leaves the Bipolar 1 with Mixed Episodes in his computer and never changes it. Ever. I think he chose that because I do in fact have Bipolar 1, and my very worst and most frequent episodes requiring hospitalizations were full manic episodes with mixed features. I do also often have euphoric hypomanias that tend to eventually turn mixed over time and at their worst. I kind of agree with him that this is a common characteristic of my bipolar disorder. Perhaps your psychiatrist changes your diagnosis in terms of episode type every time it changes? I wouldn't know that. I do believe hospitals mark the episodes as they see them during hospitalizations. At least mine have. I've been Bipolar 1 the whole time, but in some it is manic, others mixed episodes, others depression. I've had psychosis with pure depression, pure mania, and mixed states. Sometimes I don't have psychosis.

I have had mixed states that lasted hours to several months. On good medications they last days max. Sometimes my moods are all over the place. My mixed episodes are usually simultaneously elevated and depressed (high energy, impulsive, desperate).