HHF
You're correct it is totally different. The East uses the same system that all schools in the State use - for non-boundary (public) schools. And that's enrollment. The numbers are submitted to the PIAA every two years. It's male (or female) enrollment in grades 9-11 on 10/1 (I believe). So on 10/1/21 teams submit their enrollment numbers to the PIAA. That's the school's number used for classification for the following two years. It is meant to reflect your potential pool of athletes. That's also when teams could change classifications. All non-boundary (Catholic, Private, Prep, etc.) in the East are in AAA. The theory being that those schools are comprised of players from all those public schools.
The last two years the number dividing A and AA in the East was 620. The line is usually drawn for hockey at a natural break point somewhere around 600. The smallest AA school in the East is Wm Tennent (633) and the largest A school was Garnet Valley (602) during the last round of enrollments. So the line was drawn between those two schools. Norwin's male enrollment number in the last round was 620, so in theory they would have been the largest A school - or the smallest AA school. West Chester East's number was 522. The system is not subjective and takes opinion, how good you were last year, etc. out of the equation.