Here is the best image I could find about what I'm trying to relay
What your looking for is the growth on the older lateral branches, I explained the vertical whorls to try to get across what you are looking for. They're not as distinct on the branches but they're more indicative. We were looking at a predominately Douglas fir mono-culture and this was the specie that he pointed it out on.
So if your looking at a big tree, maybe around 80 years old, and the inner of the tree is all dead, and the old lateral branches have died all the way out to the last 5 whorls on the branch, then as I was told by Sepp this means the tree has roughly 5 years left to live.
I don't have near enough
experience to prove or disprove this, I'm just relaying what Sepp told us in the workshop and it makes good sense to me. I don't think it's the rule so much as a good tool to evaluate the health of a forest.