There is a tenuous lines of communication open to North Korea via China. North Koreans work in China or Russia, people also escape to China and may defect to South Korea. Some keep in touch with family back home and send money back. It's all very tenuous because North Korean government knows all about this and only tolerate it due to the money they bring in to the country. It can ends very suddenly if they feel like making an example out of few people. Story from defectors are also limited in their usefulness because they can be greatly exaggerated, or limited to their home town. The dark humor I've gotten from South Korean researchers on North Korea is that the only corroborating evidence they can collect on North Korean food situation is the number of bodies that float down the Imjin river.