Re: a7S firmware version
I confirmed with Sony that the new firmware version supporting 15.3 stops in raw is the launch version, v1.0. Sony said that some pre-release cameras may have had older firmware versions.
The DxOMark review didn't say which firmware version was tested.
I also learned something about the way DxO measures dynamic range. DxO's dynamic range is, for one pixel, the ratio of the saturation illuminance at the sensor to the darkest iluminance at the sensor with an output SNR greater than 1 dB. But then they multiply that ratio by the square root of the camera's pixel count divided by 8 megapixels. It's a way of converting a per-pixel measurement to a per-area measurement, normalizing all of the measurements to the same effective resolution and removing the noise penalty of a high megapixel sensor. The extra factor is the theoretical increase in dynamic range that you'd get from the noise reduction that comes from downsampling the picture to 8 megapixels, *if* the low end of the dynamic range were noise limited, and not limited by the luminance encoding scale. It also assumes that the image is uniform and the noise is Gaussian. So high megapixel cameras get an artificial boost in their dynamic range measurement that may or may not correspond to the the actual dynamic range of a picture downsampled to 8 megapixels.
Let's not forget that dynamic range is a real thing that can be measured per-pixel, and it has a real maximum and a real minimum. Just as there are high sensor illuminance levels above the saturation point (clipping), there are small illuminance levels that cannot be distinguished from total darkness in the camera's raw output, even if you ignore the noise. Those small illuminances are outside of the camera's dynamic range.
A 14-bit linear raw scale, for example, can never express more than 14 stops of dynamic range, even if you remove all of the noise. But there are 14-bit linear raw cameras with DxO measurements of dynamic range greater than 14 stops.