[proper_elb]

You raise a good point, and I would answer it with agree and disagree:

Agree: Yes, you are correct, merely observing that a code path was never executed in the last 6 months is not the same as understanding why the code path was created in the first place. There might be the quite real possibility of an infrequent event that appears just once in every two years or so (of course, this should also be documented somewhere!).

Disagree: Pragmatically, we have an answer if the code path was not executed after 6 months use in production and test: We know that, with a very high probability, the code path was created either by mistake (human factor) or intentionally for some behavior that is no longer expected from our software. To continue the Fence metaphor, regarding Sensenmann: After 6 months, we know about the Fence that 1) it has no role to play in keeping the stuff out that we want out (that was all done by other fences that were had contact with an animal at least once) and 2) that it might have been used to keep out flying elephants or whatever, but no such being was observed in the last 6 months (at least the fence made no contact with it, which it then should have!) and probably went away.

That said, having a human in the loop is probably a good idea.