The latest criteria declared by the JoSAA Authority are to be considered during admission process. Top 20 percentile criteria means the candidate has to overtake 80% students to be among top 20 percentile. It changes every year as the performance and question level changes.

But a student is considered to be in top 20 percentile in his or her batch only. Suppose a student passed 12th in 2018, then his or her top 20 percentile will not be compared with the batch of 2019.

If the student is in top 20 percentile in his or her batch then he or she stays in top 20 percentile. It can not be changed.

Hope you understood. All the best.