I appreciate your concern re having an idea of how numbers are arrived at. To give you an idea of how Ilford work, I am one of about 10 working photographers who are given pre production materials to use in our everyday photography and then write a report on how we rate it. Generally we are not given any information as to the characteristics of the product so we have to work it out for ourselves by testing. For example, I had Delta 3200 about 12 months before general release and did all sorts of daft things with it including rating at to 25,000 ISO just to see what would happen. The results where interesting and I now ocasionally use that rating to achieve the effect that I like. I'll post an image I made in a New York underground station with a test batch of the film to let you see the result.

I do not have access to densitometers etc but test in my own way to work out the best speed etc for myself. Certainly, Ilford listen to those of us who test in this way although I cannot speak for other companies. I hope that this posting gives you some understanding of what goes on behind the scenes.