Historically, Chrome displayed tiles. However, the backend logic often tracked the top 9 or even 12 sites, rotating them based on recency and frequency of clicks. The number "9" in mostvisited9 typically indicates the pool size from which the visible tiles are drawn.
If you are not yet seeing nine tiles, do not panic. The rollout is gradual. Here is how to check and force the update: chrome newtab mostvisited9 updated