The existing nábrók is probably a modern reconstruction, with little evidence for the original
Returning to the nábrók, NB: the surviving specimen is most likely a modern fabrication, merely reconstructing the legend. They are kept in a private museum, and since it is thanks to them that we learnt of it at all, they evidently do their work tolerably well. Evidence for the trousers themselves is very slight, and rather indirect. Well, even if it is a hoax, it is a thoroughly ghastly one. Far creepier than, say, those Icelandic spells for the destruction of an enemy's livestock.