JEE

Normalization will be session wise so the percentile score you got would be relative to the others in your session. This score denotes the percentage of candidates who have scored equal to or below (same or lower raw scores) that particular Percentile in that examination. So the 15 toppers are students who have all got the highest scores of 100 percentile after normalization in their respective sessions. The marks obtained in between the highest and the lowest scores have also been converted to appropriate Percentiles. JEE Main 2019 rank (probable) = (100- NTA percentile score) X 874469 /100
If NTA percentile score is 90.70, JEE Main rank will be (100-90.70) X 874469/100 = 81325
Consider the NTA score of 80.60 then JEE Main 2019 rank = (100-80.60) X 874469 /100. The rank will be 169646. This formula would not be for a 100 percentile score as those are the top ranks.