Siliconmaster482 said:

Personally, I have no problem with the new lines. As much as people may pretend the prequels never happened, the added lines do support the assumption that Vader did not know what had happened to his child(ren). With the old lines, it appears he already knows Luke is his son. I mean, it's up to Ady, but IMO the newer ones are one of the SE changes I agree with.

The thing is, if Vader is running around the galaxy saying "The Rebels are there, and I'm sure Skywalker is with them!" and the opening crawl saying how obsessed he is with finding young Skywalker, I'm pretty sure that unless he forgot his old last name, he knows that Luke is his son. In the original version, it could be interpreted that the Emperor is just upgrading Luke's threat level, while in the new one he's basically telling Vader that Luke exists, when it's obvious that Vader knows already.