Chrille said:
The problem comes when Obi-Wan calls Vader his pupil, and says that Vader killed Luke's father. A prequel viewer would know that Obi-Wan never had a student called Vader, and that indeed Anakin was his only student. Wouldn't that make the viewer figure out Vader's identity?
Well, yeah... okay, that still makes a mess of things. The only thing I can think of then is.. crap! Lucas, you dumb bastard!
It "could" still work, in that Obi-Wan blames Vader for killing his father... the thing is (if ROTS was edited per my suggestions), you wouldn't know that Anakin was Luke's father, since the baby boy is sent off into hiding at the end of ROTS without a name (and you don't show the Tatooine scene - just a ship flying away with the baby), and Owen was established as Ben's brother even during A NEW HOPE days, it would be conceivable that - off screen - Kenobi created a name for the baby when he gave him to Owen ala Merlin in EXCALIBUR when he was walking off with Uther's kid.
That way, when Kenobi gives his speech to Luke, we just met Darth Vader in the beginning of A NEW HOPE and who knows how many people Vader has killed since ROTS. Thus, Luke's father COULD be Anakin (due to the Prequels focusing on the 2 of them), but (1) Kenobi never says his father's FIRST name until JEDI and (2) Kenobi could have taken a second (or more) pupil(s), who was/were then "killed" by Vader.
Granted, most people (without ever having seen ANY of the STAR WARS movies... HA, HA... I know... good luck on that one) would go, "Wait a minute... Darth Vader killed his father? Could it be that whiney guy in those earlier movies? Hmm...", then EMPIRE would come along and they would see his head and go, "Wait a minute! That looks just like the scar on that whiney dude's head in ROTS! Is that the same guy?!"
So by the time he has Luke trapped on Bespin and made his reveal, it wouldn't be a total punch to the gut, but I could still see some people who, even if they've figured it out nearly all the way, just to have Vader actually say it will still have some impact.
The whole point is to TRY to develop some continuity with these things as best as possible, which is kinda hard with how HOWARD THE DUCK Lucas got with the Prequels.
Now THERE'S an idea! Replace Jar-Jar with Howard the Duck!