1956 No Shoulder Strap New Zealand Halfpenny
In 1956 the portrait of Queen Elizabeth II used on New Zealand's coins was updated to more prominently show a shoulder strap on the Queen's clothing (p72, Pepping, New Zealand History Coined, 2017) - this change occurred across all denominations but the old design was also used in 1956 for some pennies and threepences. Although no catalogues report it, there are reports of the old design being used on a very small number of 1956 halfpennies.
Jerome Remick reported the existence of at least one piece which underwent thorough testing and was found to be genuine. He also estimated that perhaps 200 such coins may exist (p461, Remick, British Commonwealth Coins, 1971), although the whereabouts of the reported example or the existence of any other pieces is now unknown: presumably the variety not being listed in any catalogues has left it and other examples as unattributed.