True..I said maybe. For one thing, I read recently in a past article (think March 2002) that Alias fans will have to think about Sloane's paternal obsession with her. The show never really got into that so maybe they'll put some insight on it soon or something. All the other things that were mentioned have already occured.
But in past conversations between Jack and Irina, she was always referring to Sydney as either his or our daughter. Maybe she's too smart to slip up, but still, you'd think if she was Sloane's daughter, she might have slipped up in some way.