But then where are the attestations? Did people not write anything in Aachen until a few centuries ago?
Yeah, you're right of course. One should look for attestations, for example the earliest attestation in a High German text. That has probably been done and I should check it sometime... But I still don't get on what you base your claim. If you say that a word died out in all Germanic languages except one, then I would presuppose that you yourself should have checked these languages for their earliest attestations. You wrote that the German word for "Maas" had died out (or never existed, I don't know). You also wrote that modern German "Maas" is borrowed from Dutch. Now if you say that you need proof, I guess. It's not me who needs to prove the contrary. And of course, if an unfounded claim makes perfect sense then I don't bother at all. (I'm not someone who says we need to quote seven books about something that is common sense.) But this is one thing that just doesn't make much sense to me (personally).-- Best regards, I'm going to bed.