Is the second part actually true though? I can't find any sources about this, in fact the opposite seems to be true. North Korea recently changed their constitution and describe South Korea as a "hostile state" which means they officially recognize it as a "state" at least[1]. Before that they explicitly had a goal for unification in the constitution which implies (or can be implied) that there never was such a view that "the entire Korean peninsula has remained united under the rule of the Korean Workers’ Party". There is also this sentence:
>This North Korean world map is centred on the Pacific Ocean, which gives Korea a privileged position on the global stage
This is normal for asian maps, Japan does the same thing for example.
[1] https://www.reuters.com/world/asia-pacific/north-korea-repor...