From the NZ Post site:
1950 Sovereigns Provisional
Due to an increase in postal rates on 16 July 1950, it was realised that the stocks of the 1 1/2d value stamp with portrait of King George VI would be inadequate to satisfy future demand for this value.
An urgent order was lodged for a further printing of this stamp, but because there was an inevitable delay in the receipt of the new printing from England, it was necessary to produce a provisional 1 1/2d stamp.
The New Zealand Government Printer was instructed to produce a stamp in the 'Arms' style. Printings were made from a plate with no value indicated and the actual denomination was applied by a second operation. The 'Arms' stamp design was completed by H L Richardson in 1929. His design incorporated the New Zealand Coat of Arms, however because of the confined space he depicted his own interpretation of the subject, which varied considerably from the version authorised by Royal warrant in 1911. An error was made in the design whereby the New Zealand flag is depicted instead of the Union Jack.
Information included on this page sourced from The Postage Stamps of New Zealand published by the Royal Philatelic Society of NZ. Their web site offers further information useful to those interested in the stamps and postal history of New Zealand. Link: https://www.rpsnz.org.nz/https://stamps.nzpost.co.nz/new-zea...-provisional
Date of Issue: 28 July 1950
Designers: H L Richardson, Wellington
Printers: Government Printing Office, New Zealand
Stamp Size: 24mm x 28mm
Sheet Size: 80 stamps per sheet
Process: Surface printed - Typography
Perforation Gauge: 14
Paper Type: Wiggins Teape chalk surfaced, multiple NZ and star watermark