At some date after the signing of the Armistice on 27 July 1953, for reasons known only to the North Korean postal administration, a decision was made to introduce an airmail fee of 75 won. That this was likely due to the huge influx of members of the two Neutral Nations Commissions (NNRC and NNSC) appointed to oversee the application of the terms of the peace settlement and the repatriation of POWs, who wanted to communicate quickly with their home countries of Poland, Czechoslovakia, Sweden and Switzerland is beyond doubt. The numbers of people wishing to use this service grew even more over the ensuing months as technical and medical specialists from Eastern Europe and elsewhere, arrived to assist in reconstructing infrastructure destroyed during the War.
What is not clear is why the specific rate was chosen when it required the use of a 5 won stamp, when North Korea did not have a stamp of that denomination and had never previously issued one. The effects of this new rate provide an interesting philatelic story that was to cover a three-year period of provisionals and flexible approaches to solving the 5 won ‘problem’.

Great article presenting first hand research on this complicated subject. Very interesting.
Thanks Florian.
I believe that the Kaesong Provisional stamp will be listed by Scott this year.
Tony
I think the most interesting cover on Figure 10 . On this envelope there are three stamps with General Pang Ho-san.
There is a good article about the stamps and the supposed fate of this military commander on the KSS website:
https://koreastampsociety.org/2018/12/19/mistaken-identity/
As a small addition to this article, I am sending a photo of an Air Mail cover from 1954. Date of cancellation: March 18, 1954. The cover is philatelic (it does not have a cancel of arrival). And the denomination of the stamps is less than the tariff specified in this article. Only 42 won.
Alexander (see previous comment) sent this image of the cover.
Tony Another great & fascinating article