"Absolutely nobody is prohibited in any way from talking about any previous stories. But apart from saying, “Hey—remember that story we published a few years ago?” there’s often no compelling reason to do so." I see your point, but I still think that Steve explaining Kang to Bucky (who should know about him anyway) as a time travelling terrorist is not a very good introduction, that's like saying: oh Alexander the Great? He's just some terrorist.