Couple of really good papers there Ekka, and raises a very important issue for any Arb assessment we can always find defects and weaknesses in every tree whether its at the crotch or elsewhere, and every tree will fail at some point given enough time or enough loading.
By focussing on the target exposed under or next to the tree we can eliminate a huge amount of unnecessary tree work, no target...no problem. Of course applying the basics of VTA every time in a systematic way and ensuring that for trees with a target we are comprehensive in the way we examine the tree..no drive bys here
A great mental tool to use at the end of any assessment is to imagine how many trees out of 100 of the particular species with the particular defect/weakness etc you would expect to see failures in a year.
So if you had 100 of these trees in the same circumstances how many would fail in a 12 month period (so that would include at least one storm season).
There are very few significant failures, even here in Oz, compared to the actual number of trees we have in urban areas, and managing the risk should follow the same established and accepted rules that are applied to risk management in every other aspect of our lives.
SF