Within a CMS Site, on the Site Statistics tab, we expect to see more data than is available. For example, if you click on the Monthly tab and choose the Month drop down, we only see data in the first month selection and the details of the previous two months are blank.
The Site Statistcis feature is a legacy feature of Sphere is not recommended for use. It was left available as a courtesy to clients, but is not a reliable source for tracking data. We recommend configuring site tracking through a third party, such as Google Analytics. The Google Analytics tracking snippet can be configured to track your CMS, per the steps, here.