In that case,
In your final answer:

""It is quite common knowledge that a freshly lube-tuned springer that is dieseling violently, to the point of achieving detonation, can be settled by shooting a few heavy pellets through it. Shooting the heavy pellets result in a much milder dieseling, which will slowly burn off any excess lubes in the compression chamber. After several heavy pellets, the mild dieseling ceases, and at that point, shooting the lighter pellets will no longer cause dieseling nor detonation. This practice that has been around for decades seems to directly contradict the theory presented in the first part of the noted statement.""

You have still failed to explain to the unknowing the process by which the dieseling "can be settled" and by which "much milder dieseling" is eventually achieved and that is: by using the heavier or tighter pellets that the chamber pressure is further increased, resulting in a higher temperature which further aides combustion and burns off the excess lube quicker to a point whereby changing to a normal or lighter pellet will no longer induce dieseling. Using heavier or preferably tighter pellets will for a time increase the dieseling effect and get rid of the excess quicker, not as implied simply tame the dieseling.
The only thing that you have said regarding this point which i can agree with is that "how could anyone know that a gun is marginal on dieseling" and i agree its impossible but is it not the theory we are talking about?
Anyway all this takes us back to the original question point 1. FACT entirely feasible in theory.

For those struggling with grasping the heavy or tighter pellet part of this discussion: Possibly the easiest bit to grasp here is if we use a tight pellet in the bore ie. one whereby it is more difficult to push down the barrel, hopefully you can see that this will increase the chamber pressure above what a looser fitting pellet will, by causing a blockage or better seal?
The heavier pellet is a bit more difficult to understand but basically heavier things (in this case a pellet) have more inertia or "reluctance to get moving" it takes more energy to get a heavy pellet moving than it does i light one, in an airgun pellet for this scenario this will have little effect but heavier pellets will have thicker skirts resulting in a better resistance to deformation in the barrel so creating a better blockage if this is easier to understand. Another way of thinking about it is this: the heavier or tighter the pellet is in the barrel breech, the higher will be the chamber pressure and thus temperature at the point where the pellet starts to move.
Hope this helps
Eric