These are some of the comments from experts on gmat club and Reddit. I don’t have permission to quote them.
Many of our understanding about percentiles are wrong. You can look it up further on google.
“A percentile divides data into 100 equal parts, requiring 99 divisions or tick marks. These divisions are called percentiles. For example, if your score is at the 1st percentile, it means all scores below the 1st tick mark are lower than yours, placing you somewhere between the 1st and 2nd tick marks. Being in the 99th percentile means all scores below the 99th tick mark (the last one) are lower than yours, placing you somewhere between the 99th mark and the end. Therefore, there is no 100th percentile.”
“99th percentile means you scored better than 99% of people — and 1% scored either the same or better.
100th percentile would mean you scored better than 100% of people including yourself, which would be impossible because - as you said - you can’t score better than yourself.
0th percentile would mean you scored better than 0% of people, meaning 100% of people scored either better or the same as you. This is possible because you could have just gotten the lowest possible score.”