In 1958, the British Post Office introduced a small range of stamps for use in the regions, Northern Ireland, Wales, Scotland, Isle of Man, Jersey and Guernsey.
As postal rates are subject to change, the designs are often updated. From 1958 to 2000, the design was a fairly standard portrait of the Queen of England. In 2001, some pictorial designs were introduced.
In the 1980s, I made the decision that “Northern Ireland Regional” stamps are genuine “Irish” stamps.