MDS CATALOGUING A FICTION WORK

Any help welcome. I always learned that when cataloguing fiction with a Dewey number, the nationality of the author drove the build of the number and yet I see Neil Gaiman's American Gods listed as 813 instead of the 823 (British Authors). Any input on which is the more accurate? I'm even seeing it in the Library of Congress. His work Neverwhere, which takes place in London is 823. I'm now confused which is correct.

Please don't shout.

American Gods

Gaiman has lived in the US for more than half his life. If you cannot choose both, then you must settle on one. Do you go with birth or country of residence?

>3 Petroglyph: Gaiman has lived in the US for more than half his life. If you cannot choose both, then you must settle on one. Do you go with birth or country of residence?

Or country of passport, for those with a residence in a tax haven....