We can trust Dear Leader.
The East Germans had the Stasi, and it was a highly regarded organization, even working with the primitive equipment (by today’s standards) they were limited to.
Because of the nature of communications back in the latter third of the 20th Century, telephone taps and direct human intelligence were employed to a much greater degree than they now are. It is possible, even with the vastly increased number of communications devices and means, to gain a statistical advantage just in terms of measuring the volume and direction of traffic, and only occasionally determining the actual content.
Or maybe I have just been watching too much of “Person of Interest”, seeing how John and Harold monitor and act upon the information the Machine collects.