In The Library Of Dreams

In Neil Gaiman's The Sandman graphic novels series, the Library of Dreams contains every book that has never been written or that exists only in dreams, e.g.:

Alice's Adventures Behind The Moon by Lewis Carroll;

The Emperor Over The Sea by CS Lewis;

Lord Greystoke On Barsoom by Edgar Rice Burroughs;

The Bestselling Romantic Spy Thriller I Used To Think About On The Bus That Would Sell A Billion Copies And Mean I'd Never Have To Work Again by an unnamed dreamer.

My daughter, Aileen, said that she had seen an eighth Narnia book somewhere in the house...

Poul Anderson must have many works in the Library of Dreams. I can think of at least three.

"As for what became of those who were still alive at the end of the book, and the sword, and Faerie itself - which obviously no longer exists on Earth - that is another tale, which may someday be told."

-Poul Anderson, The Broken Sword (London, 1977), FOREWORD, p. 12.

The withdrawal of the Fairies from Earth is mentioned in The Sandman. Poul Anderson wrote many more relevant works but did not return to this specific theme although it is alluded to in The Merman's Children.

Secondly, another non-existent title: Emperor Flandry. The plot would be that there is another succession crisis and the Policy Board invites Dominic Flandry to ascend the Throne.

Thirdly, The Return Of Aycharaych. This might also tell us what became of the Merseians.

Also, of course, entire series about Diana Crowfeather, Roan Tom, the Long Night, the Allied Planets and Rangers of the Commonalty.