To check for any gaps in register please go to Reporting > Reports > Attendance (tab) > Gaps in Register by Date.
Once in this report ensure that in the top right you have clicked to show gaps.
If you are greeted with an error message, you will need to go to Admin > Config > Core Set Up > Holidays to ensure that none of your dates are overlapping.
For further information on removing the overlapping dates please click here.
To find N codes over a specified date range, please go to: Reporting > Reports > Attendance (red tab) > Unauthorised Absences
Select the date range required and click to show only unknown absences and choose. This will show the student names, Year, form and date of the absence.