Learning from Experience
Espionage is said to be the second oldest profession. (For those who have to ask, the oldest is prostitution.) Like the oldest profession, the basics of espionage really haven't changed much over the past two thousand years. But there are a number of newer developments in the kinds of people involved, what they are after and how they accomplish the dirty deed.
Experience is the best teacher, so past cases have been selected and described to illustrate important points. Some timeless truths that need to be repeated may be best illustrated by an older case. Due to security, legal, privacy, and practical bureaucratic considerations, it usually takes several years after an arrest and conviction before unclassified information on new cases becomes available for broad dissemination.