My understanding is that the production process hasn't been fully figured out, even by the original lab. I saw some charts suggesting it took 332 tries to produce 2 similar samples.
This is a first-principles calculation known as density functional theory. it’s a useful basis for understanding physics in solids. it won its inventors the nobel prize in chemistry in 1998 iirc
I may have missed some follow-ups, but wasn't the original team Korean?
Yes, there was a paper published on an unsuccessful reproduction attempt from a Chinese team