The Nation related stamps are not Discworld, but are definitely Sir Terry and so deserve a mention here. The prize item in this collection is the framed cover sent from the South Pelagic Islands addressed to Charles Darwin at the Royal Society. The border is decorated with fantastically detailed maps of the islands. These were a quite limited edition and only available to Emporium visitors in person. The stamp is canceled with a horizontal oval frank as used in Victorian times for British post offices in the colonies. The 670 cancelation is however fictitious. The cover also boasts a paquebot stamp for HMS Dolphin. As an aside, while there have been a number of Royal Navy ships called HMS Dolphin, this title was used most recently for a cadet training school in Gosport. Moreover during World War II the German propaganda machine was said to have reported its sinking.
This item was probably originally intended for another project - the Cabinet of Curiosities. It is not meant to be contemporary with the events related in Nation. As this project never came to fruition completed items like this presentation could still be sold as single items. There may have been thoughts on a series of stamps based on the Nation world, but this may have put too much of the business emphasis on stamps.

The stamp itself features King Henry IX. Remember that Nation is set in parallel universe very similar to ours, and so it is no surprise that the royal portrait greatly resembles King George V (but with a beard like Edward VII’s). In fact the stamp bears more than a passing resemblance to the 1902 high value stamps of the Somaliland Protectorate. A part sheet held in the British Library shows that the sheet margins were essentially undecorated (apologies for the bad lighting on the photo).

Whether or not a full range of stamps from the states and countries mentioned in Nation was possible or seriously considered, there is still another stamp, and this was not made available to collectors. This was the Port Mercia One Penny. It too had an our world look-alike in the St. Lucia low values of 1882.

Having said that there was an actual Nation one penny stamp - a cinderella from our world issued to tie in with the Charles Darwin 200th anniversary stamps issued by the Royal Mail. Thus the Nation stamp is set in our time as well as our universe. Two covers featuring stamps from both issues were available.

Finally, there was a Roundworld emberella, if you can call it as such when it is not Discworld related. Whatever, it is the Dolphin stamp used on post from the Emporium during 2009. The artwork is based on a painting by Ian Mitchell. These were printed in sheets of 60 stamps, and when used could be cancelled with a Nation frank.

As a postscript there is one more stamp to mention. In 2009 a Roundworld emberella was issued to mark the 75th anniversary of Stamp Magazine, I have heard a whisper that the design used was originally intended for a Queen Daphne stamp. How true this is I cannot say, but if you look at the stamp you have to ask what is the relationship between a philatelic magazine and the Royal Standard and crown used in the design. This layout would certainly be more fitting for a monarch whose empire stretches across the globe.