Watching the movie with someone who knew the reveal, but had not seen ANH or ESB before they had a different take on it. They assumed Anakin and Darth were two different characters, Obiwan told Luke the truth as he knew it, and Lukes unnamed mom cheated with Darth Vader before he was a machine man. And the fight where Vader killed Anakin was likely related to the baby daddy drama, with Obiwan probably in the dark.
This makes a surprising amount of sense, so why did everyone in 1985 instantly assume Darth=Anakin?