I read it. It’s a great read that lays out Lucas’ evolving ideas about Star Wars and what his plans for the saga were at any given time.
When I was a little kid in the late 80s/early 90s, I recall somehow “knowing” that Star Wars was supposed to be a 12 episode saga (or was it a 9 episode saga?), and that Lucas originally wrote an enormous script, but originally only filmed the middle part of it (episodes 4-6). Kaminski’s book spells out, in painstaking detail, exactly when/where these ideas emerged, how accurate they were, and how, over time, Lucas changed his mind about various things but then basically tried to rewrite history Joseph Stalin-style by pretending that whatever he currently said about Star Wars was “the way it always was”.
Kaminski claims (with copious footnotes to back it up) that no such larger script ever existed. Only Episode 4 (originally just called “Star Wars” Episode 1) existed. However, it is true that after Star Wars was an unprecedented major success in 1977, Lucas announced plans to turn it into a 12 episode saga (meaning 11 additional movies). But the idea was that each movie would mostly be a standalone story, perhaps with a larger plot or theme tying the movies together. Then after Lucas rewrote the original script for Empire Strikes Back, and merged Luke’s father and Darth Vader into a single character, the 12 episode thing disappeared and now the official plans was a 9 episode saga. The 9 episode saga (ironically) was planned to be pretty close (very broadly speaking) to what we actually have today: Episodes 1 to 3 would be about young Kenobi, 4 to 6 about Luke, and 7 to 9 about some other Jedi character that was mentored by Luke (possibly the mystery person spoken of by Yoda in Empire Strikes Back when he said “there is another”, before that turned into Leia.) However, no actual scripts or plot outlines existed for any of these planned sequels. There were some vague notes or ideas for some of them (like Episode 1 to 3 would be about young Kenobi, there was an Old Republic, and a politician named Palpatine manipulated the Senate and created the Empire) but nothing resembling a fleshed out plot.
But then after filming Empire Strikes Back and ROTJ, Lucas was extremely worn out and went through a difficult divorce that rendered him financially incapable of funding more Star Wars movies. Still, in theory, the official plan remained an eventual 9 episode saga some day.
Then a decade later, after CGI technology had matured, Lucas decided to do Episodes 1-3. No earlier scripts existed for these movies, so he wrote each of them one at a time right before filming (in some cases writing them as they were filmed.) At this point, Lucas became very vague about the earlier 9 episode plan, eventually saying outright that the plan was always to have only 6 episodes, because no further story existed beyond that. This is when he started claiming that the entire saga was the story of Anakin Skywalker. He claimed that the “9 episode” plan was simply an invention of the media. (But this was not true; Lucas said many times in the 1980s that there would be 9 episodes.)
Ironically, the 9 episode plan would eventually happen anyway (obviously). Kaminski claims that originally Episodes 7 - 9 were to be about another Jedi (possibly Luke’s sister), probably the same person Yoda referred to when he said “there is another” in Empire Strikes Back. Obviously, after this “other” was turned into Leia, no plans existed for Episode 7 until much later when Lucas decided the Sequels would be about a young woman (some time in the late 2000s/early 2010s, before selling to Disney) who would be mentored by Luke.
Finally, there’s one alternate version of Star Wars history floating around which originated from Gary Kurtz (Lucas’ producer during the Original Trilogy). This version of the story says that there was supposed to be 9 episodes originally, but the story of Luke would encompass Episode 4 through 9 (forming a “hexology”). In this version of Star Wars history, the events in Return of the Jedi were to be stretched out over episodes 6, 7, 8 and 9. Episode 6 would focus on rescuing Han. Episode 7 and 8 are unknown, and Episode 9 would be about Luke finally confronting the Emperor. However, according to Kaminski, this simply isn’t true and Gary Kurtz is misremembering/conflating things.