1.7.2, and 3.6.5 third bullet, both say that when a Stronghold located in a City is destroyed, the attacker takes "all of the City's Prosperity as Plunder".Well, that should be a fairly rare situation (I can't remember it occurring in any of the 50+ test games I played or monitored), since cities are tough all-or-nothing propositions and enemies tend to come loaded for bear when going after them, but should the city fall and not enough attackers survive to carry off all the city's plunder, then the balance is lost (the city is sacked and the assailants burn what they can't carry off).
When there are fewer surviving attackers than remaining Prosperity cubes on the City, what happens to the excess Prosperity cubes? Do they remain on the City, conforming to the general rule that Prosperity is only plundered up to attackers' carrying capacity? Or are they removed off board, since the specific rule states that all the City's Prosperity is removed?
Note that the general rule is not that Prosperity is only plundered up to the carrying capacity of raiders, but that no unit may carry more than 1 Plunder. This is specifically spelled out to mean that the Prosperity of a Raided Region is only plundered up to the Raiders' capacity to carry in the specific rules for Raid actions I think.