That's kind of a new thing I have heard. How could a CA Final student can do such mistake. If you have written correct in numbers and bubbles I think it will be alright. While sending copies to paper checker institue removes the roll no.portion. They have the database which roll no.copy is sent to which copy checker. But writing roll no.corectly in numbers and bubbles area is very important because marks are uploaded on that basis only as far as I know.