Different combinations of film and developer have different curve configurations. Therefore it is impossible to apply a blanket model to all of them. Some black and white films will actually deliver about twelve stops of straight-line separation without resorting to "minus" or compensating development, and at the other extreme, some might only deliver six stops of range. Eight is more common. Then you have to match that to the printing paper. And I'm more concerned about the shape of the toe than the overall range per se. This isn't a religion!!! There is no one set of rules or any
silver bullet. Rather, it's a simple tool kit for acquiring negatives which are reasonably within target range to print well. One has to customize all the variablse to their own specific needs. And as an anecdotal aside issue, I once measured a whole stack of gray card from various manufacturers on a high quality full range spectrophotometer, and not one of them was even close to 18% reflectance, nor did any of them match the peak sensitivity of my light meters. So one more reason you need your own standardized reference.