I love the fact that they put Ian McDiarmid in THE EMPIRE STRIKES BACK. It makes the continuity so much better. But one thing I truly do not understand is some of the new dialogue.
In that scene now, the Emperor tells Vader that the young rebel who blew up the Death Star is the offspring of Anakin Skywalker. To which Vader replies "How is that possible?" "Search your feelings blah blah, son of Skywalker must not become a Jedi blah blah."
Sounds all fine and dandy and helps you know how and when Vader finds out Luke is his son. ONLY ONE PROBLEM.
Earlier on in the movie, when they discover the Rebels are on Hoth and there is debate between the officers as to the validity of this "lead" Vader chimes in that that is the system and he knows Skywalker is there. Now I know in real life as well as in Star Wars people have the same first or last names without being related. But how many Skywalkers could there be? And if Vader had the "young rebel who blew up the Death Star" researched, was the only thing he came up with was his name? I'm sure with the vast reaches of the Empire if he got the name of the rebel, he must certainly have gotten some more of his history. And at that point Luke's only history was being raised on Tatooine by the Lars family. And even if all he got was the name, wasn't the name enough to make him have Luke researched some more?So my question is when did Vader know.
I believe somewhere (possibly the ESB commentary) Mr. Lucas tells us that he wants to show when Vader finds out. But it is clearly obvious, to me anyway, that Vader already knew based on the afforementioned dialogue with his officers.
Now, I personally believe that the real-world reason for this is George Lucas wanted to change Vader's finding out from offscreen (between episodes IV and V) to onscreen (in episode V) because now having made the prequals it adds a little more drama, and this earlier bit of dialouge was an oversight. And what George Lucas wants, George Lucas gets. So the new Emperor scene probably is the true canon where Vader finds out. But what is the in-universe explanation for him knowing his name and not putting two and two together?
And my personal feelings are, if George changed it from offscreen to onscreen and that's now officially how Vader finds out, then when he releases these dvd's again, the first line must be altered or deleted. Because otherwise it makes no sense. Unless the explanation is, the side of Vader's brain that remembers his own last name got burned on Mustafar.