Hi Steve,
It would be quick unusual for the belt not to have had at least one change.
It's quite easy to remove the top cambelt cover and take a look at the belt condition, but perhaps for peace of mind you could come to an arrangement with the dealer that they will pay a percentage for the cost of a new belt.
I'd expect around £350 inc vat for a belt change from a good independant in your neck of the woods, but it's always worth spending an extra £70 (ish) for a new waterpump and coolant while the belt is getting done.
If any of the services in the service book are from VAG dealerships, they will have a record on their computer system of all work carried out by VAG, so you might be able to track down a belt change.
Anything you need, let me know.
Cheers
Jeff