Moodle Course Completion

Extracts from an email thread, S asked the question and answered himself - 

...we have a custom report 'Course Completion Status' in one of our Moodle instances.

There is a field 'Course Completion - Completed' and this field should show 'Yes' when the course is completed and 'No' when the user is still doing the course. And then there is another field, 'Course Completion.Student Progress' and this field shows the percentage progress.

For (one particular) course many teachers have completed the course (the percentage is 100); certificates have been issued to them. However, the field 'Course completion - completed' is set to 'No' and not 'Yes'. What could be the problem? Even the system report 'Activity Completion' has all the activities ticked. 

Found out the issue - within the course, the course completion criteria weren't set up. To mark the course as completed, at least one criterion should be enabled. 

In the course page - More->Course Completion, enable one or more conditions. I have enabled 'Custom Certificate-Course Certificate'. And immediately, all the people who have received certificates have been marked as 'Completed'.