Now that you mention it, I do remember reading three buttons needed. But, NOPE no buttons here. I thought at the time that one shoulder might button but it doesn't.
When you get to the neckline it tells you to seam one shoulder, make the picot edge then seam the second shoulder. If I were doing this again I would seam BOTH shoulders and make the picot edging in the round, I think it would make for a nicer neckline.
The neck opening is large enough to pull over a babys head. I have no clue what the buttons are for!!