This ignores a bit of history, at least in the Cold War for Russia and China. Assets were basically use once and burn. Agents could realistically last maybe 12

This ignores a bit of history, at least in the Cold War for Russia and China. Assets were basically use once and burn. Agents could realistically last maybe 12 months in either place and could never return. The youngest would get deployed because they had the cleanest records. Russia mostly knew who the experienced spooks in the consulate were, even using cover.