It is easy to increase our knowledge of a fictional world. The author needs only to write something new. Anderson's last novel to feature Dominic Flandry reveals for the first time the prior existence of two communities, the Dakotians and the Zacharians, and also tells us how earlier events in the Technic History had affected a man named Magnusson. Thus, earlier history is recapitulated and re-presented from a different perspective.
So far, I had found only three religions in Jerry Pournelle's Second Empire of Man. However, nowhere in the texts was it stated that there were only three religions and the sudden appearance of a man named Singh raises the possibility that this history also incorporates Sikhs. But not necessarily: googling the surname (here) reveals that it is not after all exclusive to Sikhs. Thus, although Pournelle has raised a possibility, he remains free to develop the hint in any direction he wants. (He probably does not intend to pursue the issue of Singhs but you never know!)