I’m assuming you’re referring to current versions of TESB? In the original 1980 film, Vader had already learned the name (and identity) of the pilot who had destroyed the Death Star and was hell-bent on tracking him down (for obvious reasons). The notion of the Emperor telling Vader who Luke was during the hologram chat was one of Lucas’ post-1997 tweaks and, typically, doesn’t make a shred of sense.
As Screams said above, Marvel had Vader learning Luke’s name during a raid on a Rebel stronghold. TESB as it stood merely left it to the audience to wonder how and when Vader had learned Luke’s name.
As for the opening crawl, I think it was just a way of defining Luke as a rebel leader rather than the naive farm-boy of the previous movie.