The site here says it is 9 vol. (ongoing) yet other sites say 7 vol. (complete). Can someone explain?

A manga adaptation, drawn by Satoru Nagasawa, was serialized in the Japanese shōjo manga magazine The Margaret between October 2003 and December 2007. It has been collected into eight bound volumes released by Shueisha. The story in each volume follows the corresponding volume of the novels.

In 2010, the manga began serialization again by adapting the "Cherry Blossom" story.