The Voice is a thick, rich, dense show. It has many layers, kind of like an amazing cake.
The blind auditions — the first layer, as it were, and the feature that originally made the show STAND OUT — are taped months before the show actually airs on NBC. The battle rounds and knockout rounds are pretaped as well.
Then we get to the icing on the cake, the live shows. The Voice works in advance in other ways, too. For instance, during the live shows for Season 3, The Voice films blind auditions for Season 4. Which means that as of November 2012, Blake Shelton and Adam Levine are working with Christina Aguilera and Cee Lo Green on live shows at the same time they are working on blind auditions with Usher and Shakira, who will be taking Cee Lo's and Christina's chairs on the first 2013 season.
Let's hope no one gets confused! It would be embarrassing if Adam were to call Shakira "Cee Lo."