I was questioning your claim of "surprisingly large" double defectors not that there are defectors. 13 out of ~1600 is not a significant number. Your second source is not relevant.

>"In one case, a double defector re-entered North Korea four times."

Constantly sneaking in back forth is a common thing from the documentaries I've watched. 1. People stealing goods and selling them back home 2. People stealing supplies to feed their family back home .