I know it has been all seniors but that doesn't mean that juniors would lose a season if they competed. They have scores of events in the off season that don't disqualify underclassmen from competing. And you did not address the private school question.
Piaa eligibility booklet - Google it, easier than me linking it. Article IX section 2 All-star contests, can also do a search of the document for "allstar". Not sure if this covers the PWC or not. I'll also let someone else interpret what that means exactly. But does mention a loss of 1 year of eligibility.