For reference, here's the Japanese version of the text.

ロウェナ : ……そうね。隊長格の蛮族が持つという「蛮神刻印」3種類を、それぞれ3個……それから「敵性民族教本」を持ってきたら、交換してあげる。
I had been assuming that we needed 3 of each, but after seeing the English version, I'm a bit curious. Is the NA version just a mistranslation? Or did the developers change their minds at the last minute and not get around to updating the JP text?

Also, if it is just 1 of each, then why aren't the items marked as unique (they're currently just untradable). Of course, if it's one of each per weapon, then being non-unique still makes sense (though it seems a bit harsh given the drop rate).