That type of thing was pretty common in spy novels. No idea how common it was in practice. Depends on the author. Some authors are well-known for the thorough

That type of thing was pretty common in spy novels. No idea how common it was in practice. Depends on the author. Some authors are well-known for the thoroughness of their research. Some spy novels have been so accurate that ex-intelligence people have approached the authors to ask them how they knew certain things, and to offer them more information that would be useful for new manuscripts.