Having spent last evening at an election results watching party, where I got to explain to bunch of politically-savvy people, who figured they'd have known if anyone, exactly why we won't get to know the final result on the referendum until December 10, I thought I'd go through it here.
The Electoral Act 1993 governs the counting of votes in a general election, and it requires that on polling day, all the advance votes are counted, and all the votes cast on polling day are counted and a provisional result is announced. They don't count special votes, and they don't do the checking to ensure that no-one voted twice, but they give everyone a pretty good idea about the result.
The Electoral Referendum Act is different: it required local returning officers to count the advance votes (which they can start counting from 2pm), but forbade them counting normal votes on election day; instead of individual polling places conducting a preliminary count, they must instead send the voting papers to the returning officer before they are counted at all. The Act requires that each returning officer count the referendum votes "As soon as practicable after the parcels of referendum voting papers are received by a returning officer."
I'm not entirely sure what that means, because despite advice from the Electoral Commission that they won't be releasing any results until the final official count, I don't see that it prohibits them from releasing a preliminary count of the ordinary votes in the days after polling day. A final result - waiting for overseas votes to reach New Zealand and the like - will take as long as the parliamentary elections, but it seems pretty practicable to me to count the ordinary referendum votes in the next few days.
The count of referendum votes is a lot easier than the count of general election ballots: the usual protections of traceable ballot papers weren't imposed, so even if someone double-voted, all their referendum votes will count, because there's no way of finding the ballots they cast. Even the protection of scrutineers was dispensed with, and with the requirement to get the votes to the local returning officer pretty quickly, there's seems to be no reason after the "as soon as practicable" count is completed, why a fuller preliminary count couldn't be released. The law may not require it, but it doesn't ban it, and the principle of open government, and transparent elections, seems like an excellent starting point.
A final note about special votes: it has been pointed out in comments in other places, but bears repeating, that the numbers of special votes listed for each electorate are the number of special votes cast in that electorate. These may be special votes from people who aren't on the printed electoral roll (because they're on the unpublished one, or they enrolled after the rolls were closed for printing), but they also include votes cast within that electorate in respect of another electorate. In an electorate like Auckland Central, which has a lot of special votes, many will have been cast from people in neighbouring electorates who found it more convenient to vote while in the city on Saturday.