Much of what was planned for the sequel trilogy was condensed in to ROTJ from what I read.
After Empire George went off the idea of making Loads more Star Wars films as it nearly made him bankrupt and his divorce and so on.
Return of the Jedi was the ticket George needed to Set up Skywalker Ranch and all the companies in the franchise.
So there was probably a new sequel trilogy written later. But most of it is in ROTJ