Ruminations of a Star Wars Geek
I spent much of the weekend mulling over various inconsistencies within the Star Wars movies, now that the series appears to be complete, as Revenge of the Sith left a few open issues that could not be reconciled on their faces. So then I went to the deuterocanonical sources...the Star Wars novels I read back in the 1990s. And they may provide some insight.
A few issues...
The Death Star was under construction at the end of Episode III, but it appears that it may have taken about 20 years or so to build (Luke and Leia are at least 18 by then, but not much beyond that) which is when it becomes operational and a known threat in the galaxy. But there is a gap of time of about 4 years between Episodes IV and VI, after the Death Star is destroyed and the new one is under construction over Endor. Granted, Death Star II is by no means complete by Episode VI, but it is certainly operational. So how do we get from a 20 year project to one done in about a fifth of the time?
Perhaps construction technology has advanced, but more likely there is an even better answer. In the novels, all Lucas-approved, the Empire has an undiscovered outpost near Kessel (yes, the location of the infamous spice (read "drug") mines) which is located in a gap between a series of black holes in the region called "the Maw". . It's in a series called the "Jedi Academy Series" by Kevin Anderson. The Maw installation contains a fleet of Star Destroyers and at least one Death Star skeleton ready to be built, years after Episode VI. Perhaps there was simultaneous work going on for both Death Star units of Episode IV and VI, as we know that the structure of Death Star II is significantly larger that Death Star I. The skeleton may have been just dragged out for construction at Endor. The Emperor probably moved it there (rather than being in the relative safety of the Maw) so that the Rebels would find it an attractive target and thereby lure their fleet into a trap.
Of course, in his cockiness, the Emperor, like the Jedi in the first three episodes, believed what he wanted to see when saw visions of the future, and the rest is history.
But the whole "prefab" notion of the Death Star may be a decent explanation.
Another problem is Leia's memories of her mother in Return of the Jedi that do not comport with Padme's death in Revenge of the Sith. I have early memories, but I find it hard to believe that memories of birth stay with you. But remember this: Padme's funeral was of the open casket variety. Also, she still appeared pregnant, which is an obvious ruse for the benefit of Vader and the Emperor and the protection of Luke & Leia. But if that was faked, is it possible that Padme didn't die at all, but rather went to Alderaan to care for Leia, and then later dying from the broken heart which seems to be the case in Sith? She possibly would have avoided Tattooine for fear of being seen and/or the memories of Anakin's start towards the dark side after the death of Shmi Skywalker.
It's all a bunch of conjecture, of course, and I should not have to do Lucas' explaining for him, as he has had years to turn these movies into perfectly consistent works, given his plenary creative control over them. But it's an explanation anyway. Please forgive this disturbing display of useless knowledge.