The HTTP status code specification is 30 years old, fully documented, and widely misimplemented. The misimplementation is not ignorance — most API developers know that 200 means success and 404 means not found. It is the edge cases where the correct status code requires a moment of thought that the wrong choice gets made, and the wrong choice gets propagated to every consumer who must now handle an error that does not mean what the specification says it means.