Board Thread:Naruto Discussions/@comment-1018594-20160409062530/@comment-4849011-20160816162132

A retcon is when you go back and change something that had already been established (like when Yashamaru went from being a chunin to an ANBU). A continuity implant is when you add something that doesn't change anything (like when it was revealed that the Sage of Six Paths had a brother helping him combat the Ten Tails). If anything I'd call Kaguya a continuity implant rather than a retcon.