I agree the coolant is best to be changed at some point... and that point is when (not if) the cooling system needs something serviced. I DISAGREE that there is a published specification for changing it: because there is not. That is all I was saying. VAG DOES consider the coolant in their vehicles to be "lifetime" and never needs to be serviced. The semantics of that word "lifetime" can mean different things to different people.
In the VAG world, most all of these cars will need something on the cooling system touched before they are 10 years old. The ones that tend to go the longest (and I have a good dataset for this) as I mentioned are the later 2.5L 5 cyl gas engines in the A5, A6, NCS, NMS cars. These have no timing belt. These have no silly plastic housing nonsense water pump assembly like the craptastic EA888 4 cyl gassers have. These have no variable collar water pump that breaks apart like the later VR6 cars have. These have a reasonably simple cooling system overall. The most common reason they have to tap into the cooling system is when the quickie lubers and mouth breathing morons overtighten the oil filter caps to the point they crack the plastic oil filter housing and it starts spewing oil all down the front of the engine... THEN you have to open the cooling system because not only do you have to take the front of the car off for access (which of course means removing the radiator), but the oil cooler is attached to the side of the oil filter housing. So unless you are going to collect and reuse the coolant (which nobody outside of California is likely to do), it is going to get replaced. However, in those circumstances, the coolant is still perfectly fine. There was never any issue with the coolant to warrant its replacement "just because" in the same manner there is no reason to replace the coolant when you replace the water pump preventative wise on a timing belt job. It just gets done be default. It is like replacing the air in a tire when you dismount it to patch a puncture.
BTW, there are ways of measuring coolant quality. One universally used way is to measure latent voltage in the cooling system. It is an old school but effective way of testing, but modern HOAT coolants generally are very good about not allowing this to be a problem, so it is not often thought of much any more.