How to explain the KGB's success identifying CIA agents in the field

https://www.salon.com/2015/09/26/how_to_explain_the_kgbs_amazing_success_identifying_cia_agents_in_the_field/

What Totrov came up with were 26 unchanging indicators as a model for identifying U.S. intelligence officers overseas. Other indicators of a more trivial nature could be detected in the field by a vigilant foreign counterintelligence operative but not uniformly so: the fact that CIA officers replacing one another tended to take on the same post within the embassy hierarchy, drive the same make of vehicle, rent the same apartment and so on. Why? Because the personnel office in Langley shuffled and dealt overseas postings with as little effort as required.

As soon becomes evident on reading, the fact that Totrov was able to produce telephone book-size volumes of CIA and other intelligence officers for KGB chief Yuri Andropov testified to the structural defects within the U.S. government in the relationship between its key operational departments in the sphere of foreign policy. All Totrov did, once apprised of this crucial flaw, was follow through schematically and draw out the pattern. This was human intelligence of the highest order and an acute embarrassment, once known, to those responsible for the conduct of U.S. foreign intelligence.

Jonathan Haslam is the author of "Near and Distant Neighbors: A New History of Soviet Intelligence," which was just published.