Hey,

See the answer keys are released by various coaching organisations and not by the official body conducting NEET examination. Often it happens that the original answer key has certain changes, there may be some confusion regarding some MCQs . So the answer keys released immediately after the exam are not 100% correct. Thus there sometimes occurs this marks difference between the calculated marks and obtained marks.

Also the papers are checked with extreme caution by the NTA and there is no room for mistakes . Hope that clears your doubt.

All the best