Octopus Books publishes a range of books that are set in the Tolkien legendarium, from coloring books through to a range of books by David Day. They are widely available online and through retail stores (at least here in the UK). All of these books have a disclaimer on the back that says 

> This work is unofficial and is not authorized by the Tolkien Estate or
> HarperCollins Publishers.

At the same time, according to Wikipedia

> The Tolkien Estate maintains the position that the geographical layout
> of Middle-earth or any other places in the imaginary universe created
> by J.R.R. Tolkien was the intellectual property of J.R.R. Tolkien and
> subsequently is that of his heirs. The Tolkien Estate has therefore
> restricted the publishing of maps to those authorized by the Estate
> and legally pursues anyone who publishes any maps, including self-made
> works, on the Internet.

Granted, that's primarily related to geography, but how does Octopus Books get away without a substantial lawsuit against them? Some of Day's books have custom maps in them. Surely a disclaimer is insufficient?

Btw, I asked the same question on the law forum of Stack Exchange and the answer was basically that maybe the Tolkien Estate hadn't noticed, which seems highly unlikely.