Ok, we're a bit off topic now, but let's see if I can explain what I do: average white person as subject. Black backdrop. Using ISO 400 film. If I do an incident reading at EI 400 I will get a good exposure of the skin, but my black backdrop comes out dark gray. If I overexpose, yes, overexpose by at least one stop I then get a lighter than normal face, but I print it down to normal in the darkroom and then I get a black background.
It might not make sense to you, but it works.
In my 1st post I meant to say, "No perfect dev. No perfect film"
"It's not the age, it's the mileage" Indiana Jones