1. I don't think he originally envisioned the character Qui-Gon Jin when he was making the OT.
2. I doubt he originally envisioned Anakin being conceived by midichlorians or growing up as a slave
3. I'm not convinced he knew Vader was Luke's father when he made Star Wars or if Luke and Leia were always brother and sister
4. I really don't think he originally envisioned Boba Fett's daddy as the man who was cloned
5. Is there any way he originally planned to have Padme die when he wrote ROTJ and Leia said she remembered her mother?!
6. Didn't he originally envision a tension between Owen and Anakin as well as tension between Owen and Obiwan? None of this was developed in the prequels. Heck, Owen met Anakin AFTER he had left Tatooine and "gotten involved." There was just no impression that Owen thought Obiwan was a wacky old man either. I mean the dude gave him Luke to raise!!!!
7. Nobody can convince me that George had visions of trade disputes and Jar Jar Binks 30 years ago
8. There is no way he originally envisioned Greedo shooting first. I mean, Han was clearly loading his reched blaster
9. If Anakin wanted Luke to have his lightsaber when he was old enough, then why didn't he ever say anything
10. The terms "Padawan" and "midichlorians" were absent from the OT, so how could this have been part of the plan?
There's plenty more I could come up with, but I really think his so-called vision was never really clear.