Never mind about the Legendary Western Armor. It's just a bit of dumb coding.

Apparently if you have multiple materials but only one meets the lv. requirement (thus showing only one in the selection), you still have to select that one.

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^ Having said that I had problems (invalid code) making another forge stone right after. So I guess that's not what's going on here?

I reloaded the game and managed to make it so I guess it's buggy.