This is pulled from a Danzo comment on the forums over 2 years ago.

1) in that NPC, you can do three things. 1. Farm materials to craft skillbooks. 2. Use those materials to craft skillbooks. Note: any duplicate skillbooks c*so be used to craft skillbooks. 3. A treasure of skillbooks and you use seal scrolls. Nobody except for the mods will tell you when this update will come. Just look out for the update on Wednesdays when they do announcements.

I'm mostly just looking for somewhere to trade in my duplicate skillbooks and possibly work for Mei skillbooks without having to use coupons for fragment buying