Yes,  i understand your query regarding this as i would like to give you a brief about this as follows :

As there are two rounds to held for councelling, round 1 and round 2. Admissions for there rounds takes place for candidates who have registered for it and according to their choice preferences. Now all the seats which are left vacant during the first two rounds, for them a mop-up round is held. Here its like first come and first serve, the seat will be given to any candidate present who have qualified the exam.