Radio Corporation of New Zealand was formed in 1932 and finished up in 1959 when they sold out to Pye (N.Z.) Ltd.
Originally known as W. Marks Ltd, RCNZ became one of the largest radio manufacturers in NZ.
In around 1937, with the introduction of the house brand Columbus, RCNZ started moving away from producing 'private brand' sets and within a couple of years was only manufacturing receivers under the names Columbus and Courtenay.
RCNZ built a lot of their own components in-house, including capacitors and speakers.
Date codes used on Columbus and Courtenay sets are based on the first digit of the serial number. A set with the serial '07213' would have been manufactured in either 1940 or 1950. a holistic approach is required to determine which decade, but in most cases it is reasonably easy to figure out based on valves, cabinet design, technology, etc