Behavioral equilibrium by type can emerge even when strangers cannot identify each other

Evidence

The population ratio P has not entered into the equation so far. It has an interesting role to play if its value lies between 1/6 and 1/4. Consider any value in this range. Then it is clear that in addition to the two equilibria we have already identified there is another, where each person of type 1 chooses X, and of type 2 chooses Y, on every occasion. At this equilibrium it is common knowledge that type 1 people are always honest and that type 2 people always cheat a little. But at no encounter does either party know who he is dealing with. Behaviour according to type is therefore what emerges at this equilibrium. — Diego Gambetta, Trust - Making and Breaking Cooperative…, 873

Categorization

• XREF: Directly extends Luhmann’s ‘familiarity without identification’ — strangers can sustain type-based behavior through reputation even when individual identity is hidden. Core to the reader’s Luhmann/Hardin synthesis.
• DEFINE: Shows how a stable equilibrium can arise purely from common knowledge of type proportions, not individual recognition.
• QUESTION: When does the society actually gravitate toward which equilibrium — the follow-up paragraph flags this as unresolved.