The import dialog includes the option "Create or Update PI Points" which I had taken to mean that any PI Points defined in Af would automatically be created in the associated PI Server if they are already defined. However by way of answering a differet but related question it would appear that my assumption was incorrect. Having run a few tests with and without the "Create or Update PI Points" option checked it would seem that it necessary to right click on the attribute or containing element and select "Create or Update Data Reference" in order to create or update the PI Points in the PI Server. Per chance I have a copy of the PI AF Templates V2.0 document which on page 19 confirms what I had though should happen rather than what my 'experiements' reveal.
But perhaps I'm misinterpeting something?