Also, that first treatment from 1973 is just Kurosawa’s Hidden Fortress retold as a space opera. It wasn’t until the first draft of the script that Lucas started making his own story and Luke Skywalker and Darth Vader appear. It isn’t until the second draft the droids appear and characters start to take on familiar names and the story starts to resemble the final version. Luke and Leia were cousins in that draft and Luke had brothers. So lots of family connections in the early drafts and then nothing in ANH with revelations in TESB and ROTJ. As Lucas always intended the ST be made this decade (per a quote from Mark Hammil about episode 7 coming out in 2011), that means a long gap between trilogies so holding the revelation of “the other” until the ST makes no sense. He got the fans buzzing after Empire so it makes sense his plan was always to reveal the other in Jedi. Why make them wait for 30 years. No, when you put the fact together - the early drafts, the secrecy about the family revelations during production, the meaning of names, the stories of fake scripts to catch anyone leaking the plot - it all adds up to the story as we got it was planned from the get go. They weren’t last minute additions - they were secret plot points that weren’t included to keep them secret.

That’s not to say that the story didn’t evolve. Han in Carbon Freeze, Lando, Boba Fett, the second Death Star, the location of the final duel, Ewoks, and a host of other things came about during the evolution of the scripts. But the basic story, the one that evolved from the early drafts and that he had to break up to make it filmable, that remained intact. I am positive that in that final draft of A New Hope, Lucas intended that Vader was Luke’s father and that Leia was Luke’s sister. Ben’s story about what happened to Luke’s father being labeled a lie in the novelization coupled with Alec Guinness’s acting in that scene in the movie make that story of Vader betraying and murdering Anakin a lie, just as Ben admitted in ROTJ.