The true Breaking of the World!
Yes, that's what I was thinking, similar to how the Aes Sedai have lost the ability to make ter'angreal until Elayne figures it out, but damane were able to make a'dam, which are ter'angreal.
Try to smash it? lol
This is wild speculation, but: maybe the ability to make cuendillar wasn't lost before the establishment of the damane system, so they had a non-zero number of enslaved channelers who could produce useful trade items (UGH I really dislike the Seanchan).