Star Wars Darth Vaders memory

Well I guess he was pretty busy over the years hunting down the remaining Jedi, building an Empire, mourning Padme, and solidifying his position as the Emperor s right hand man, but you think Darth Vader would have remembered C3PO. You know the droid he built and his last surviving link to his mother. Who died in front of him and made him turn evil. Guess he moved on.