How can he not be on Roger`s ship without us knowing? we don`t know his full biography, who says he wasn`t a pirate before joining Moria? Roger was sick yes? and all of Rogers pirate went into hiding, who`s to say he wasn`t on Rogers ship as an assistant to that other guy that stood in reverse mountain? i honestly wouldn`t be surprised if Oda does something like this, this is One Piece after all.