Luck also matters a lot, I am going to share my experience, in Environmental science, I paid not a cursory look on ES related to Pakistan, such as PEPA, and national disasters management authority, thanks God, and by luck;it was not in the question paper.
Now move to the opposite:
In criminology, I studied very extensively, but skipped the techniques of investigation and methods of collecting evidences, unfortunately it resurfaced in the paper.(my precious 20marks in the hell!)
This is the reason why I'm saying this 20marks checking criteria is highly subjective and nonsensical as well.sone pe suhaga, 12 papers aur her paper men same substandadard approach, at the end we don't know the mood of examiner as well,for example I was strictly forbidden not to write against the establishment and against the prestige of the "national interest", which according to me ,itself is a diabolical term to give a blanket cover to the self interest of politicians.