Oh right - I hadn't missed that, thought there might be something elsewhere. Given those words are setting aside and replacing the standard going requirements, I think that is clearly intended as a statement that the requirements for tapered treads are those on the diagram (going on centre line, tread on inside). I don't think the two together can sensibly be interpreted any other way. But, it's not a law.
If your local BO disagrees, wind him by saying it's just guidance and not binding anyway. (Maybe not).
Edit: Also 1.27 makes no sense unless 1.25 is saying there is no going requirement on the inside, just a tread requirement. Otherwise, your inside 50mm going in fact has to be as wide as your going on the straight treads, and that way lies madness. In 1.27 therefore, the going requirement for the tapered treads has to mean a single (centre line) going requirement. The reference to a going requirement cannot be different as between 1.25 and 1.27 (or it would have to stipulate in 1.27 just the centre line going to exclude any separate inner going requirement). Accordingly, the inside tread requirement in diagram 1.9 has to be separate from the single centre line going requirement for a tapered tread.