Here are a couple of photos. I thought they might have been where the cable was on the floor in a small pool of water where the rain had dripped off the car in the garage. But some are near the charging plug and would never touch the floor when charging - see the second image where the brown spots are slightly out of focus because the phone focussed on the floor not the cable which is nearer.
If that is an overheating / burn mark then I would think trading standards would like a look at it. It should not be possible for a suitably specified cable to overheat when run at its design capacity so that IMO suggests there is serious problem. If any more appear then a recall could be needed.
I took the cable to the local dealer. They thought it was faulty and are sending it to VW. They think there is evidence that the cable had been run over. If so it was done at the original dealership - it was a demo car with 1007 miles on it when I bought it. There's no way I would have run over it the way I stash the cable after charging, but whether they believe me is another question.
I have to use a public charging station now as I've only got that cable. However as I've never done this before I'm looking forward to the experience. Just took a photo of the other cable to see what I need to know about selecting appropriate charging points. Already got zap-map on the phone and I've located 3 reasonably local points.