Guess it depends who you talk to. When I did my original IR test around 12 years ago the examiner (UK CAA) was very clear in stating that under the regulations in the UK the 'approaches' were complete at the DA / MDA, if you went around then that was the Go Around Phase, if you continued to land then that forms part of the landing assessment i.e. you can fly a perfect ILS to the DA and then cock up the landing, that would be judged as a pass grade for the ILS but a resit for the landing assesment.
So in answer to the above I would consider that the approach starts at the IAF and finishes at the applicable minima, in the case of a CAT III that would be at wheel touchdown when NO DA.