Why do you find it so difficult to understand that the shows are recorded well in advance of their transmission dates. The soaps are recorded weeks ahead as is Countdown - one of the few live quizzes is Brainteaser on Ch.5 where you can be put through to the studio during the course of the game.
I think they record 3 D or N Ds in a day so when someone's been there for 27 shows, it's not so bad, only 9 days. Sometimes Noel gets the day wrong which is quite amusing. With such a large audience and all the contestants, plus the winner herself, it's not difficult to imagine that someone would talk about the big win. Maybe the TV company itself let the cat out of the bag for the publicity.