Ticket Count Discrepancy Btw Two Reports

Former Member
Former Member $organization

I am settling a completed performance with no reserved seats.  The Ticket Sales by Period and the Performance Sales Summary are agreeing in total dollars but not in number of seats.  Performance Sales Summary by PT Category his higher by a small number of seats.  I think the issue is some paid seats (not comps) are being excluded from the Ticket Sales by Period count although I cannot be sure.  My question is what triggers the seat being included in the Ticket Sales by Period total?