The Korea Stamp Corporation, the stamp issuing organization of the DPRK (North Korea), generally creates stamp along several lines of themes. One of those common themes is something along the lines of “the eternal fight for the motherland against our enemies”. The thing is: the official feelings towards these enemies, whomever they may be (usually the US and/or South Korea), come and go.
Since it takes time to create a new stamp issue, sometimes the KSC finds itself in a position where the KSC is no longer in line with the official narrative. This is politically speaking impossible: the North Korea state simply can’t be wrong! And since the KSC is part of that same state, this means the KSC can’t send a message which is different from the official narrative.
So what to do as KSC when you have just created a nice stamp series showing, in beautiful and striking colours, something along the line of turning Seoul into a “sea of blood” or hitting Washington with some menacing looking newly developed missiles? Simple: you disown them. The usual trick is to simply ignore the fact these stamps (or other philatelic items, such as postcards) were never issued.