So after result, many of my seniors are getting 100 marks

So after result, many of my seniors are getting 100 marks less or more than what they calculated from these so called answer keys. One guy got 86 correct from marrow but 98 from Nanwani . And in the final result, ended up getting 108 correct according to his marks. So, my question is , WHAT THE EFF IS HAPPENING??? How can So much difference be there? I mean facts are facts na??