It can't be the people who took the same test in the same room because that wouldn't be a statistically significant sample.
I know for SATs & ACTs the curve & percentiles are calculated based on scores of a group who takes the test before it is released. Who that group of people are, no one seems to know. I imagine that's how the percentiles for DAT are done.
It does seem strange that 23 for some sections is 99th percentile. Less than 1% get between 24-30?