Ken, thanks for sparking the discussion. :) I think that in this case, what was within the “official” doctrine of the Church and what exceeded it is of less importance. What is historically significant is that the practice of selling indulgences was wide-spread, commonly associated with the Catholic Church by the people and — from what I understand — often tolerated by the Church’s officials. The sentence just after the one you quoted:

“With the permission of the Church, indulgences also became a way for Catholic rulers to fund expensive projects, such as Crusades and cathedrals, by keeping a significant portion of the money raised from indulgences in their lands.”