Board Thread:Spoilers!/@comment-27060727-20161201052050/@comment-25375217-20170110174315

Technically speaking, every flashback is a "retcon" because "retcon" means "retroactive continuity". Any time they introduce a past event, they are creating a retroactive continuity. It only becomes a problem when that retroactive continuity specifically clashes with a previously established retroactive continuity, like in Swan Song.