User blog comment:Xilinoc/Ch. 556 - The Wolfsbane/@comment-5695542-20131106184407/@comment-11051098-20131106234847

As far as I can see from chapter 101, Tobiume had 1 prong on the upper side and 1 on the lower side, while the anime showed it to have 2 on the lower side. I suppose Kubo either decided that 2 looks better, or had her train intensively after Aizen's defeat and her Shikai developed a 3rd prong during the training.