Issued today in 1962

Tonga. Centenary of Emancipation. Issued 7 February 1962. A sheet of each of the 1s and 5s was issued with the overprint inverted in error. The affected 5s sheet was discovered intact (meaning up to 60 examples exist) while the 1s sheet was predominantly used for first day covers. Very few unused examples of the 1s exist.