Treevet, no worries; no offence was taken! We got quite a chuckle out of it, because we do indeed lay awake at night thinking about these things.
You expressed your thoughts very well. We are not sure what Ekka is thinking because it sounds like he is saying that without callus growth there is no Wall 4; and yet in pictures by Gillman, Shigo and Mattcheck they all point out Wall 4 being at the growth ring immediately after the injury. Which in future years will have healthy growth outside of it. However, callus growth is outside the tree at the point of injury and doesn't extend into the tree (with the exception of occlusion at the edges of the injury).
The study that Ekka sited in his last post was referring to debarking while living cambium remained attached to the tree. That in itself makes things a bit confusing as it is not the only time Wall 4 is activated.
So just trying to clarify these thoughts in our own minds as well.
D and S Mc