Thanks, Ryan
The reason there are so many names is that on the two sides and the back side the names record those who served, not those who died. The only ones who died are those on the front of the memorial under the heading 'these men died for their country'.
In fact a recount shows that there were 48 who died, not 47; and according to the Auckland Weekly News the memorial was unveiled on 22 September 1923, not 1922. The report in that paper also says that 47 were killed, so either they could not count or one name was added later (but that does not seem likely since the names are in alphabetical order).