Sixth World Almanac will bring you up to 2072. After that, the books covering major developments would be Emergence, Ghost Cartels, Artifacts Unbound, Conspiracy Theories, WAR!, Spy Games, Dirty Tricks, Hazard Pay, Clutch of Dragons, and Storm Front, as well as the season 4 Missions, and so on. Still, for basic understanding, I'd say you can limit it to Sixth World Almanac, Artifacts Unbound, Clutch of Dragons, and Storm Front. You'll be skipping a few things, but that'll get you the major stuff.