Stamps of half cent denominations were withdrawn in 1971 and the same year, the inland postage rate for first class mail was raised from three to four cents. This produced increased demand for the four cent stamp, while large stocks of 2½ cent stamps remained (previously the rate for second class mail was 2½ cents and this had increased to 3 cents). Many sheets of the stamps both imperforated and perforated were sitting at the printer in England, while others sat in Post Offices around the country.

To handle the three different cases required three different processes, which resulted in three varieties:

The imperforate sheets were surcharged in England by photogravure (recess printing) after which they were perforated and cut into sheets in the usual way. This stamp has two thin horizontal bars and can be distinguished from the other two varieties by the high quality of the photogravure printing process and the screen dots which give the diagonal portion of the 4 a stepped or almost digitised effect under a magnifying glass (177a1 - left-most in the photos).

The stamps that had already been perforated at the printers could not be surcharged with photogravure as the gripping edges had already been trimmed so they had to be surcharged by letterpress (surface printing). This stamp is the most easily identified as the horizontal bars are thicker and fairly poorly printed. (177a2 - middle in both photos)

The stamps distributed around Post Offices were returned to the New Zealand Government Printer and surcharged locally by letterpress. The local print stamp also has two thin horizontal bars but can be distinguished from the recess printed stamp by the poor quality of the letterpress printing process. (177a3 - right-most in both photos)