How do we know it has affected far more than 50% of these cars ever sold?

Poor choice of materials - yes. And if they failed early on Jag did help out some customers in the warranty period (and a bit beyond). But yes - it makes a big difference that it is cosmetic. If it was a potential safety issue, then it would be taken seriously and likely fixed. But a bit of leather coming up on a dashboard of a 10 year old car just doesn't strike me as something that any manufacturer is going to pay to replace for free

You could say the same about plastic coolant pipes - or the water pump (I would suggest that far more people have had coolant water pump failure than bubbling dash) - clearly not the best part. But if out of warranty - then you have to address it yourself.

Just my view. Think it's important to be realistic about expectations - else you will have a very disappointing ownership experience.