Sone ask about those 1934-35 doubleheader attendances of over 45,000. How did it happen?
First of all, fire laws were more lax in those days. So if they oversold the bleachers, you can always fit a few extra rear ends in each row (and in the aisles).
Second, back then, bleachers and pavilion seats (a concept you don't see any more, common back then - unreserved grandstand seating) -- when someone left, they could resell his place. They would count those leaving after game 1 (or anytime) and then take someone else's money and let him in.