During an interview with the regional AO at the LAC that my daughter ended up going to, the AO told her “We know your high school school and we know that kids who come here from there tend to do well here.” She went to a small, good (but not particularly rigorous or competitive) private school in an urban area. So, anecdotally, there may be some informal tracking going on, perhaps in particular with smaller schools where the AOs have time to get to know high schools.