Some workers claimed that they could judge under safelight, and others claimed that they could only see it when a few drops were sacrificed on a glass slide and brought into the light. At the time I joined Kodak, they had ceased using this method about 30+ years earlier when the controlled digests and dual runs went into effect.
Also, for the pages Kirk gives, there is not much to see there, as he talks of the methods in general terms for the most part. I would not try to make a photograde colloid using his instructions, such as they are. They are mainly guidelines.