Sami is Brady's little sister....huh?

So I think it was last week or maybe the week before when Sydney was first kidnapped.  Brady finds out that his bailing out Nicole was an awful idea since she essentially stole Sami's baby.  He was standing in the Brady Pub and he says "I can't believe I did this to my little sister!".  What?????  Brady isn't that much older than Belle and Belle was kidnapped by a teenaged Sami when she was an infant.  How can Sami be his little sister?  Rewriting history again.