Given that:
1/ nobody has access to any hard date regarding durability testing of belts,
2/ Audi advice has been inconsistent and variable over the years,
it becomes a matter of opinion and experience when a belt should be changed. I would prefer to change the belt too often rather then too rarely despite the high cost, because the consequences of belt failure are vastly more costly. Others may choose to delay the change as long as possible and risk a wrecked engine. How lucky do you feel?