Well, pretty mundane response really. Anyone associated with the AOP B as an investigator was given a large grey note book so that case notes, ideas etc., could be recorded and referred to in later reports or if there was a query. By 1980 there was only myself and Franklyn Davin~Wilson. Following his death in 1983, I had to become the official sole investigator, though I had been acting as such since 1978.
Here is my Grey Book.
below: notes on alleged abductions.
I still add to the old Grey Book. Other than being nick~named "Quatermass" by some people I prefer the "Grey Bookers" and that made someone comment, jokingly (based on the USAF Project Blue Book), that we were "Project Grey Book" and the name stuck early on.
There you go.