Today, in the EGF pro qualification game between Lukas and Stanislaw today (Chinese rules, 7.5 komi), KataGo made a surprising claim about M19 being a losing move for black. It turns out the reason is that under Chinese rules if you have a ton of ko threats, you can sometimes gain an extra point by delaying winning a final ko, as I believe was discussed in another thread on this forum too that I don’t recall the title of at the moment. This endgame turns out to be a fascinating case study of that.
Basically, if the dame parity allows you to get the last dame, AND you have so many ko threats that you can refuse to finish a ko until after all dame are filled (even if the opponent captures the ko in between every dame, you still have enough threats) then you can gain an extra 2 points.
Here is the analysis. One of the variations has a wonderful tesuji by which black manufactures a ko out of thin air, purely to be able to pull off this trick.
EGF1-2.sgf (11.3 KB)