When you do big parties like that you don't just randomly distribute servings. I'd have the overfull, 100% real, ten minute old OJ for the guy with the really particular request and could end up serving sunny delight to the cheap seats. To serve 700 people a drink takes a considerable amount of time in and of itself so you have more breathing room than you expect.
This is really common. When you do a wedding the bride and grooms table gets the best looking portions you have, the table next to the bathroom isn't so lucky.