Many different types of philatelic products have been created over the years by many different organizations and individuals. In China the so-called “Non Postal Value Souvenir Sheets” are one specific example of a type of such a product. They were (and are?) created on a very large scale, but they are relatively unknown outside of East Asia.
D&O Trading (Zuidhorn, the Netherlands) have a very comprehensive listing of these sheets. Interestingly, there are also sheets directly related to Korea. It is easy to find them by searching for them on the D&O website. Most of the examples were created in relation to the 2002 FIFA World Cup held in both Korea and Japan.
But with 2019 being such an important year in Korean history this depiction of the Taegeukgi in the PhilaKorea 1994 logo simply couldn’t be ignored:
This is how D&O lists this particular sheet:
Unfortunately Ton van Doornen from D&O Trading when asked for more information regarding this sheet answered that despite the high serial number suggesting many were produced he doesn’t own this sheet himself. If anyone has more information (or other examples!) please leave a message in the comments below.
I do not have any of these Cinderellas, but not uncommon for exhibitions, especially for stamp exhibitions. Sometimes that put out private issues like this one, and sometimes they overprint legitimate souvenir sheets. Australia exhibitions, and overseas exhibitions with Australian participation do it all the time and can become popular with collectors. Here is an example of a cricket exhibition Cinderella https://www.ebay.com.au/itm/AUSIPEX-1984-CRICKET-cinderella-miniature-sheet-x-7-Mint-Never-Hinged/352791894572?hash=item5224091a2c:g:XfwAAOSwXWRdfzNk&frcectupt=true Here a is one at a Chinese exhibition overprinted on a legitimate souvenir sheet and sold by the Australian Post with the overprint: https://www.ebay.com.au/itm/2016-CHINA-2016-ASIAN-INTERNATIONAL-STAMP-EXHIBITION-MINI-SHEET-MUH/193157204096?hash=item2cf9110880:g:AMMAAOSwls5Y7MOl Here is another was was authorized to be overprinted for an Adelaide stamp show, I don’t know how collectors keep track of all of these, as every major stamp show seems to issue either private or overprinted S/S https://www.ebay.com.au/itm/2017-AUSTRALIA-ADELAIDE-STAMPEX-2017-SHOW-MINI-SHEET-MUH-SPECIAL-FORMAT/193157205467?hash=item2cf9110ddb:g:aEQAAOSwCtJaLlTv&frcectupt=true