I just got done reading its wikipedia page, and there is a bit of trivia that says that Threepio has a line in the book where he states that Darth Vader knows all the code words and commands to shut him down. Of course, the trivia hints to the later revelation that Anakin Skywalker built 3PO, and I have to admit that makes sense. But obviously that plot point did not exist in any way at the time this book was written, so how exactly would Darth Vader be so intimately aware with 3PO's programming? Is it explained at all?