Through a TUV customer care operator today I contacted VW customer care.
This is what he wrote to me:
"As I said, the registration document is not responsible for that issue. It tells you only how many seats in the car is installed, not how to use them. The usage is a decision of the manufacturer, so the manual is the leading document in the issue of CRS
I don´t know, where the customer care got his information from, but he mentioned a table and there were crosses. And in your case, the cross was there and it means “not allowed”
“Not allowed” means, you can´t use them, as there are some technical issues, which don´t fit.
The guy said, it can be, that the airbag on the roof (the curtain) is in the 3rd row, where the C-Pillar is, so at the lowest point, that it effects the 3rd row if there is a CRS mounted. He didn´t say, that there are airbags. But it was only his assumption, and as you wrote, there are a lot of assumption."
That is. The VW customer care don't know why and they cannot find it out.
Thank you all, ciao, Lorenzo