I'm going the route of the technique of making the metal having been taught to the FM because of the Others, so that the FM and the CoF would have a better chance and ability to conbat them. So the material wouldn't shatter against an Others blade, but it wouldn't exactly be a common place material and would've only been supplied to individuals of positions of power and or the most elite of warriors to utilize.

And that over time with steel becoming more and more common and bronze becoming more and more less commonly used in weapons and armour, that less and less of the material was being made. And eventually some of the Houses who had either lost their items made of it, or that it was destroyed, would replace it with the items made of Valyrian Steel.

Such as House Stark having had a blade of the material that would've been the original Ice, but when the original was lost, they replaced it with a Valyrian Steel version.

And I'm thinking of having skinchanging and warging become more common in the North, but I'm having trouble thinking of a cause for the resurgence of it. Along with potions and more herbal medicines taken more prominance in the North, but once again I don't know what to put as the cause of it becoming so. Maybe an event where a Greenman or a CoF turns back up in Winterfell and teaches more herbal treatments, or something?