North Island uploaded in changeset 7157537, 2 Feb 2011 (HB).
South Island uploaded in various changesets early Feb 2011 (HB).
HB 21 Aug 2012: re-approved for the Antarctic.
Note there is snow_poly too, but looking at the stats they are near 1:1 in vertices and feature counts, so strongly suspected duplicates, although a geo-comparison should be made I guess.
linz def'n: "To keep the database in line with international entity specifications the areas of 'snow and ice' have been separated into two objects. Snow and ice have been treated as coincident objects." Since they are coincident, maybe needs layer= too?
Perhaps delete the snow_poly layer all together?