Thanks JandM, for your quick reply and advice, we've actually thought pretty much along the same lines.
My wife sent a message via the INZ website's message system as they don't seem to have an email address?! Hopefully we get a reply from this, the one time I tried calling the international phone line, I was on hold for over three hours, so don't feel like doing that again(but I will if it's the best way to contact them).
You make a good point about crazy processing times, my wife's visa was all done in about a month we must have been lucky.
Hoping that some forum members have had a similar situation, and have altered their last-use dates.