>>3563046No, I'm not saying they cheat anything. That's literally the entire process for making "ISO" on a camera. A manufacturer has complete and utter freedom to do whatever they want to their signal path and the resultant output under ISO 18844:2017. Some choose to use pretty noticeable noise reduction straight out of the ADC. Others (like Olympus) opt to provide a completely clean data stream right off of the chip and leave NR up to the end user. You might call that "cheating" on the side of the manufacturers that apply NR in their signal paths but it's not really cheating, since there are no "rules" that say you can't preprocess your RAW output on the ADC side however you want. As far as proof, no manufacturer publishes their ISO methods (which should tell you a lot), so you have to go by RAW output and experience in knowing what NR looks like.
Pic related is a good example. On the Olympus, you can see that the noise looks very sharp, and the blacks and dark grays are much darker. This is what zero NR looks like. On the Sony, you can see the noise is a lot softer and the blacks and dark grays are much lighter. This is what NR in the signal path looks like. The grays and blacks are lightened because they're doing chroma reduction which Gaussians away the dark pixels, and the noise is soft because they're doing chroma blending.
Again, it's not cheating, it's just literally completely up to the manufacturing what they want to do to make any given ISO look however they want. Sufficed to say, there IS NO SUCH THING as a standardized ISO output and therefore all comparisons of ISO output between manufacturers or even camera models by the same manufacturer are completely useless.