The Grade Summary page shows an overview of all marked Assessments, Spreadsheets, and Marking Schemes.
For assignments, these statistics are calculated for all complete groupings, whether or not the grouping's marks have been released. When there is a completed remark request, only the remark request grade is counted in the statistics. These statistics count each grouping once, even if there are multiple students in the grouping.
For marks spreadsheets, these statistics count all active students that have at least one grade in a column, whether or not the marks have been released. Put another way, the only students that are ignored are the ones that are inactive, or have an entirely blank row (no marks entered).