It comes and goes in waves, plus North Korea recieves aid from China and some other organizations.
It's not "just Western propaganda," this is from the sources from North Koreans living secretly in Manchuria. There are networks of the ethnic Koreans there sheltering those who do make it across the more lightly patrolled border between North Korea and China.
Videos from North Korea... the school children are skin and bones, their level of starvation attempted to be hidden by "stage makeup" that are applied but they look so ridiculously scrawny. And this was in a video that the North Koreans prepared to try to impress us...