Additionally, the number of NKers defectors in China is high - they aren't rare.
Experience with defectors from other countries, such as the former Soviet Union, shows they sometimes tell the truth, they sometimes tell false or exaggerated stories, and they sometimes tell half-truths. I don't know why North Korean defectors would be different.
> and their accounts of starvation, extreme poverty, and harsh authoritarianism all support one another.
This specific claim is about people going to die in droves to caves, not just about harsh authoritarianism or extreme poverty. That's why it must be considered skeptically -- because it seems just like the kind of thing we're prone to believing about North Korea given other news, but this is not enough to make it true. And once it gets repeated uncritically, it becomes the "common sense truth".
They weren't going into caves to die, quite the contrary, they were going into the caves to survive.
1: https://www.scientificamerican.com/article/do-the-eyes-have-... 2: https://en.m.wikipedia.org/wiki/Mass_psychogenic_illness#In_... 3: https://en.m.wikipedia.org/wiki/Lenin_was_a_mushroom
People love shocking stories, so there can be real financial benefit on making up the wildest things up and then selling your story to media or publisher.
Defectors won't know any of this. It's expected that some would exaggerate unverifiable details, to ensure their safety. That wouldn't diminish what they actually went through.
Defector accounts are actually often inaccurate or exaggerated. North Korean testimonies often fall apart: https://www.theguardian.com/world/2015/oct/13/why-do-north-k...
One of the incentives is that they make money, or gain a visa, through such testimonies.
Back in the days when China was poor, many Chinese defectors or political refugees were actually economical refugees. They made up exaggerated stories in order to get a visa on the grounds of political asylum.
Also to fit into their new environments. Everyone loves to hate on the enemy country. You might see that in the US with some Chinese Americans online, easier to fit in. Want upvotes, just go to Reddit, say "i'm chinese and eff china". Plug in North Korea and get more sympathy.