In today's world, "dynamic range" (DR) has become, in the minds of (many) photographers one of the main characteristics of a digital camera.
Unfortunately, the public data on DR is limited to "DD - ISO sensitivity" graphs and tables. With this, the nature of noise (for example, random noise, banding) isn't accounted for, however the noise character is important for visual quality.
In reality, any practicing photographer knows that the degradation of the image in the shadows (or because of low exposure) happens gradually, there is no strict demarcating line. It's just that with the lowering of exposure, small details disappear, the contrast between bigger details diminishes, color fidelity becomes worse. Depending on the quality demanded of the image (which will depend on presentation size, viewing distance, other viewing conditions such as screen resolution, etc.,), the practical dynamic range for the specific camera will be different, even for the same ISO setting.