I've been growing "Insuk's Wang Kong" since the OS traded it to me & others in 2007. The first 3 grow outs were very successful, and until last year, I considered it to be very reliable. But my grow outs the last two years have been dismal... only 3 seeds last year from a 20-foot row (!!!) and just barely more than what was planted this year. In fairness, 4 of the last 5 summers have been abnormally wet (2 records broken), including 2020 & 2021. I've been growing runner beans for seed since 2005, with 100% success - until the last 2 years, when none of my runner beans have done well. I'm still unsure of the cause, although weather is the likely reason for this poor performance.
There has been a lot of incorrect source info posted about Insuk's in SSE & elsewhere. Gardenweb member Jim Wright was the original source; "Insuk" refers to his Korean wife's nickname, "Wang Kong" is "king bean" in Korean. His original strain contained white beans as well; but because I was able to eliminate those by selection in one generation, several of us who grew Insuk's believe that it was more of a mixture than a land race. Most of the white has since been eliminated, including by Jim himself. Others have selected for the all-black, with mostly favorable results. I've kept my strain as a balanced mixture of mostly-purple seed & black seeds. Like the OS, we eat them as shellies... but I've observed that the black seeds seem to be more flavorful.
There is a long-running thread on Insuk's
here , with a lot of historical info from the first years of its distribution. Another thread, about my early search for methods of using runner beans, is
here . (I was a newbie about cooking runner beans then, and it shows

). I'm still searching for the original thread posted by the OS, where he freely offered seed to anyone interested; I will post it here if I find it.