Hii,

I passed out from the same board CISCE Council For The Indian School Certificate Examinations.

So, i believe i can answer your question.

You said it correctly ICSE or ISC board offer 2 marksheet to its every student.

But the main preference goes to the marksheet in which the marks are written not grades.

Grades are just the range which defines your marks comes in which range

Like equal to  above 90 they offer A grade..

For 80 B and like wise .

So, you can fill the serial number accordingly.

Fill in which marks are written because marks one is only going to be considered.

Hope this will help you,

All the very best!!