I have now had a reply to my question from the government authority (Land Victoria).
” This office would take the view that all boundaries defined as Interior face, in these circumstances, would take the same principal that applied to the interior of the building and would apply to the balconies etc. “
So it looks like in Victoria, for plans of subdivisions registered from October 2011 that use Interior Face, the outside terrace/balcony tiles and any waterproof membranes are not common property. They are therefore the owner’s responsibility to repair and maintain. The POS would have to specifically state it if otherwise.