I think they had some kind of armour that looked like the depictions in the carvings - it wasn't just a different way to depict mail. We have no clue how it was made or even what it was called. If we don't know what it was called, we can't use any of the texts to give us an idea of its performance or construction.
It is certainly depicted differently from mail.
There is an entire class of armor made in this way, not just with triangular plates. It may or may not need a new modern name for the type, so we can refer to different "weaves".
People focus too much on the Shan Wen Kia. The name is too limited as it is a modern name that refer only to the armor with the triangular plates.
You're right though, that we don't have physical evidence of it, so I will move on to another topic as I have derail too much.