Based on my fine-tuning experience, I wouldn't try to do anything to that detent tab or notch on the miter gauge, as most likely, one will make it (any inaccuracy) worse, and there is also a risk that the fine-tuning can never be successfully done as per the manual unless the miter gauge is replaced.
There is no question that not all KS 120s are produced and put together exactly the same, because so many things (including the laser settings) are done manually. Even with the QA in place (which is not bullet-proof as we all know), each machine must come out the factory with one or more slight differences, and that is why we have tolerance level.
Perhaps the observations brought out by Pooman can be related to the KS120 people for further investigation.