1935, Original issue, May 1st. On single "NZ and star" watermarked paper. Found in two colours 'Green' and 'Deep green.'
1936. March 20th change to multiple "NZ and star" watermarked paper. Found in 'Green' and 'Deep Green'
1937. July. Overprint type 03, Multiple watermark.
The 1/2d official was withdrawn on the 28th of Feburary 1938, giving it a relatively short span of issue. Very rare on cover.