It's happened to us all before: You run your campaign, pick a random winner, and approve the winner.
...then you realize that the winner can't claim the prize. Maybe it turns out they're ineligible. Maybe they just never respond when you try to award the prize.
It happens. That's why you can draw new winners if needed for a short time after your campaign ends.
You can draw new winners for up to 7 days after your campaign ends. After this 7-day period, you will no longer be able to select new winners.