Recently when I bought some stamps from a Korean dealer through Ebay I received an envelope with some very recently issued commemoratives on it. This time the same seller went further and not only used the most recent stamps issued, but he actually created an FDC while doing so!
The stamps are from the independence movement commemorative sheet, numbered KPC3331-3334, which come in a 4×4 souvenir sheet.

Because space was needed for my address two stamps were taken from the sheet. This however meant that the cover would have been underpaid for 410 won, which is why the meter mark has a value of 410 won. This meter mark also doubles as registration label (see RR code) and airmail label (“Air Printed papers”). It also shows the date as 06.08.2018, which made me realize this envelope was sent on the actual first day of issuing!
And indeed, after closer inspection I noticed something about this envelope: a combination of cancellation types!

Notice both FDC cancellations and standard postal cancellations, showing the same date of 6 August 2018. Since some of the FDC cancellations are on both the stamps and the envelope one must conclude this was all done during what was effectively normal postal transit, the FDC cancellation was not some pre-cancellation on the sheet itself.
Something else I didn’t know but now noticed because of this cover: Korean FDC cancellations are city specific. The example FDC cancellation as published by KoreaPost on their website shows a Seoul Central (서울중앙) cancellation, but this cover has an Anyang (안양) cancellation.
The contents of course were what I had paid for to begin with, but this was quite a nice bonus!
I received exactly the same type of envelop with these commemorative stamps. Interesting though is that the date on the cancellations, the commemorative one and the Anyang one, are dated 2018.8.10 so 4 days after the official release. Apparently it is possible to adapt that date on the commemorative cancellation?
Anyway the sender is quite likely the same as from which I bought some stamps.
By the way did you notice that one of the stamps shows a housefront in The Hague? There is the Yi Jun Peace Museum!
Yes, I did know about the museum. In the near future an article will also be published regarding Yi Jun and the museum.
However, the fact that the date in the cancellation can be changed is surprising, especially given the fact that these cancellations are unique to the occasion. Why then make it possible to create different dates? It’s not as if this was going to happen more than once.