This issue has come to the fore when we started testing against our real courses with 100's of students.
When exporting it is possible to specify new/regrade only.
However even if this option is chosen all students who are in the course are listed in the Preview irrespective of whether or not they will be exported because they have the 'new' or 'regrade' setting. This is confusing.
The actual export does only include 'new' and 'regrade'.
So please could the Preview match the export.