Wageslave: The first thing that struck me was the Nr warning described as "intermittent". That surely is significant. An intermittent Nr warning suggests Nr alternating just above and just below the min limit (whatever that is). It does not seem to indicate a single failure to reduce collective, ie a failure to establish an autorotation. It is far more characteristic of someone milking the Nr for range to the limit.
Very interesting observation!
I found (albeit for a EC135 P2+) :
low rpm warning at <= 97%
minimum transient (<20s) power on rpm to be 85%
minimum cont. power off rpm is 80% (at GW < 1900kg)
At what low rpm would the airflow over the blades begin to stall, assuming max. range "gliding attitude", with 3 people, police gear (FLIR?) and low fuel ?