I haven't seen mention of a situation like yours before on the forum, so I think you're probably going to have to ask INZ your question.
However, some thoughts. You say "to make it up to two years which is standard", but actually, I can't see mention anywhere of two years being a standard length for a partner-sponsored temporary work visa. On the INZ page here
http://www.immigration.govt.nz/migra...milystream.htm, it has this (my bolding).
If you have been living together for 12 months or longer,
we may grant you a work visa for up to a maximum of two years.
If you have been living together for less than 12 months, initially we can only grant you a work visa for up to 12 months. Later you can apply for a further work visa for a total stay of up to two years (including the time already granted on your initial partnership work visa) if:
you and your partner want to stay longer in New Zealand and can show us that you are still in a genuine and stable relationship, or
you apply for residence as a partner.
Then, it would be much more hassle to apply for Residence under SMC than to apply for partner-sponsored Residence. For SMC, your qualifications, work experience and employment all have to be proved and checked out, whereas for partner-sponsored Residence, it's only the partnership, which INZ has already accepted is genuine, so you would simply have to show further proof that you are still with your partner since the previous application was registered. (I'm assuming you have been with your partner for a minimum of 12 months, or you would not have been expecting to get a two-year temporary work visa in the first place.)