Writing blooper

Am I understanding this correctly, but did Tracy reveal to Norman at the end that Ms. Spool killed his father in a jealous rage and kidnapped him when he was a baby? If that's true, then why in Psycho IV did Norman tell the story to the radio deejay of his father being stung to death by bees? I know IV was a prequel, but was psycho III not suppose to have happened? It seems unreal that he's be recommitted after psycho III then get out
again. He didnt look that much older than what he did in psycho III.