I would assume that they used the "Sanguozhi" (Records of the Three Kingdoms) by Chen Shuo and, of course, the novel "Romance of the Three Kingdoms". I personally believe it's based more on the novel then the records by Chen Shuo, but that really doesn't matter.
If you want to read them, try the Kongming Archives (
http://kongming.net/), especially the encyclopedia (
http://kongming.net/encyclopedia/), many of the sources have been translated by the community, and most of the major officer' biographies have been translated.