You almost need a magnifying glass to see it, but in The Mystery of the Great Pyramid, the worker Abbas (Blake in disguise) is the only person on the archaelogical site wearing his turban done exactly like Nasir, a discreet clue to his real identity.
The Valley of the Immortals is set during the end of the Chinese Civil War and features a couple of Nationalist Chinese supporting characters among Blake and Mortimer's allies. Since the book ends with the newspaper's articles about communist victory in China, the fate of those characters is unseen but grim.
