There are more Kukkiwon poomsae after 4th dan of course, but it's not clear to me that there's much significant new technique after 4th dan? I guess my larger point is: if you showed me a 5th or 6th dan doing (say) a Side Kick vs. a 4th dan doing the same technique -- I'm not sure I could tell the difference between a 6th dan performance and a 4th dan performance. So to Andy's comment, what makes a 5th dan a "real" master in some people's eyes, but a 4th dan only a "junior" master? To JR137's point, you could argue that the difference is how much you've contributed to the art. To Dirty Dog's point, you could argue that the difference is one's depth of understanding. I'm not saying I disagree with these distinctions (because I don't disagree), I'm saying: I'm not sure why somebody would view 5th dan as necessarily being more "masterly" than 4th dan. For example, a 4th dan dojang owner is probably contributing more and thinking more about the art than a 5th dan hobbyist.