As I know you are already aware, the Australian and South African branches of W & H were just that, colonial retail outlets of the parent company, whereas the New Zealand set-up was a separate firm working under licence from W & H. Thus, the Sydney, Melbourne, Adelaide and Cape Town branches merely displayed and sold products sent out from Sheffield (with no doubt employing capable labour for engraving, re-finishing etc.). The silver products sold from these branches were likely English hallmarked, as they would have met the requirements of the assay office as being presented to them in as near as possible finished state, then re-finished at Sheffield prior to the export.
We know from Peter Inchbald's statement, that W & H sent to NZ goods in a 'semi-manufactured' state and thus these items were unlikely to bear English hallmarks and would perhaps be marked locally.
The New Zealand business must have employed their own team of working silversmiths to finish work, and no doubt these same silversmiths also made items, especially those needed in a hurry, as orders sent to England would take weeks and weeks to arrive. If a replacement simple plain napkin ring was needed, then why would you send for it from the other side of the world?
So many of the big corporate names haven't got a clue of the history of the firm's they own today. Gone are the days of employees with 30+ years standing who had an interest in the company that they had devoted their working lives to. Nowadays they are run by accountants etc, who 18 months ago were working for someone else, and in 18 months time will working again for someone else, to stay longer shows a 'lack of ambition' and thus saving the history of these once great names is left to oddballs like us. :))
Somewhere, I do have piece with W & H New Zealand marking, I'll dig it out and take some images of it.