In my game when I went into the outfits I found I had the previous Assassin's outfits in with the rest. I assumed this was because I had played the previous games (didn't complete Assassin's Creed 3) and they got unlocked because the game picked up their save games.
When my dad went to play the game and went to his outfits he didn't have any and he's completed Assassin's Creed 3. the only difference between his profile and mine is that I have an x-box live account which I use to update the game on his 360.
I am wondering, what unlocks the Previous Assassin's outfits?
EDIT: To clarify (as I didn't think of it) I have never used UPlay and always skipped any signup/log in step.