When the Union was created on 31st May 1910 there were no new stamps available to use,
indeed the new definitive stamps were not issued until more than three years later.
The death of Edward VII shortly before the inauguration of the Union meant that there was a
flurry of activity changing the designs and the monarch’s image on the stamps across the British Empire.
The solution to this delay was to continue to use the current stamps of the four states, Transvaal, Natal, Cape and O.F.S.
Then, in a notice dated 19th August 1910, it stated that all the current Edwardian stamps could be used throughout the new Union.
Hence we see stamps of the Cape used in Natal, O.F.S. and Transvaal and so on for each state’s stamps
Certain values are hard to find used outside of their “home” state, this is especially true of the high values.
Transvaal was the only state to have issued postage dues so these were used throughout the Union.
The first Union dues were not issued until 1914, but one can find Transvaal values used into the early 1920s.
For a stamp to qualify as an Interprovincial it must have a full, readable date falling between 19th August
1910 to 31st August 1913, as well as the town or village being identifiable.
The introduction of the King's Heads issue on 1st September 1913 brought the Interprovincial period to an end, however
Pre-Union Edwardian stamps were not demonetised until 1st January 1938 so they can be found used on mail until then.