Terminology can't be that new. I was a VO (as described by sarsteph above) more than once more than 20 years ago and was called the Visiting Officer then .... in fact I shouldn't say "was"....
....... as the (very good) OC A said to me at the time "Being VO is a job for life......"
We must have gone full circle, because until recently it was the Assisting Officer, now the VO. The VO receives no formal training, just a brief and a video.
The Notifying Officer is the one who first notifies the NOK.