CDA finally replied to me. They said percentiles between different test sessions cannot be directly compared, and they do not indicate the skill level of test-takers.
If the score is supposed to indicate our 'skill level' I find it hard to believe in past tests, HALF of the test writers were more 'skilled' in biology that the very best performers in Nov 2018. Was there a different in test difficulty? Shouldn't be, since dental schools will receive applications with DAT scores from various sessions so they should be comparable. Calibre of writers shouldn't differ much between test writes so I don't buy that we are all less skilled in biology or PAT than past writers in the last few years were.