I have been collecting stamps from North Korea for about 30 years and I can say that the philately of this country has many secrets and mysteries. The main catalogs (Scott, Michel, and Stanley Gibbons (SG)) do not provide complete and reliable information. The catalog printed in the DPRK gives distorted price information. Yes, this is very strange, but it is a fact.
For example, one of the two rarest stamps in this country 20ch green Rose (1946, Korea Stamp Corporation (KSC) catalog #1b) costs 170 dollars according to this catalog, Michel (2014) rates this stamp as 60 Euros, Scott (2017) has no information about stamp. But if you want to buy this stamp and have a couple of thousand dollars in your pocket, no one will sell it to you for that money, because this stamp for “60 Euros” is a big rarity.