1563 may be correct number.

As per NTA and supreme court 1563 students have filed petition for time loss and was given grace mark. But being a offline exam if in a class a single student face a time loss it is possible other student also face time loss .In a class approx 20 students will be there ,so i think nta has also awarded grace marks to the other students in the class ,which may be 1563 x (16 to 20 students) which they are not reveling