In JEE advanced top 20 percentile is always there, when you go through the josaa counselling process you will get to know that. But there is little change in it, for those who score less than what it needs to be in the top 20 percentile a minimum of 75% marks is required in boards to go on with the josaa counselling. It means if you fail to get into top 20 percentile then also you are eligible for counselling unless you have scored equal to or greater than 75%in your boards(cbse). I hope now you will not confuse about 20 percentile criteria. All the best for 2020.