I don't know of any written information, but I just got my Surface replaced in July and it was over 2 years old. I went the Microsoft store and they immediately swapped out old Surface Pro 4 for a brand new Surface Pro 6 free of charge. They said if anything else spoiled then it would be considered out of warranty, but since the bulging issue is a safety concern, it is covered under a separate extended warranty.
thank you very much for your reply. I've been trying with my Austrian support for a month now to get a replacement laptop. But they say the warranty has expired.