"there are 4 known arkentools" we know of three (-dish, -hammer, -pliers)
the unseen fourth is out there as well as any that aren't currently known, this battle is showing us the major players in the titan's game and the board isn't fully set yet...

I agree when TB4GK ends, we're probably going to see erfworld: book 2 quest for the arkentools or something equally as inspiring for the title (unless parson goes home with a job well done)