I guess because some people have affective disturbances before showing the psychotic side of the illness, while others have first the psychotic disturbances and the disturbed affective episodes apear later.

For example, I have had psychosis since 11, but I never had an hypomanic, manic or depressive episode until 13.

I am not diagnosed with schizoaffective but I have psychosis, affective disturbances and suffer from dissociation, so I am a bit schizoaffective-like. Right now my diagnosis is Psychosis NOS, I am still being evaluated.

about being diagnosed firts with schizoaffective and later with bipolar or depression, It could be because the bipolar or depression was with a lot of psychotic symptoms, but they later saw psychosis only happened only during an episode.

and being changed to schizophrenia after being diagnosed with schizoffective could be because some people wtih schizophrenia suffer from affective disturbances that are not severe or clear enough to be affective episodes, but they could look like one, also, there is post-psychotic depression after a psychotic episode in schizophrenic people that's not the same than schizoaffective depressive subtype. Some people with deorganized symptoms may look hypomanic if they laugh, talk fast and incoherently or look happy in every situation while it's not an affective disturbance but an emotional deorganization.