Lars Andersen
Lars Andersen is Danish fast-archer, who stirred the archery waters some time ago. He performs quite impressive tricks, and his video is what brought me to fast archery.
It is hard to make out Larse's technique from the videos, and he himself does not describe it. In videos (which are clearly made from pieces in a longer time period) he nocks by different styles. Usually the technique is best visible there where he does something different then his fastest technique. Folowing is about his fastest technique.
Arrow storage - in the string hand, between fingers held by end of arrow.
Separation of arrows - none; arrows are already separated between fingers, it is not necessary to separate them. However I expect that he pulls the nocks of all other arrows away to the palm by thumb, and the one that should be nocked is fixed by the thumb to guide it better on the string.
Nocking - by a pull, from the outside of the bow. I expect that he makes a rail from the thumb, but it cannot be seen anywhere. String hand ends in "mediterranean draw from the outside", sometimes quite deep.
Drawing the string - he holds it exactly in that mediterranean draw that he ended in. Both hands do the draw. When he wants to be really fast, then it is draw mostly by bow hand, if he needs to hit, he uses string hand more.
Speed: ~ 1 arrow in 0.5 seconds
I am not sure about the arrow separation and rail from thumb, the rest is for sure.
The biggest advantage of the technique is extreme efficiency, which brings great speed. The biggest disadvantage is unreliability - nocking itself just has to be trained enough.
My imitation and description of technique