There is a fascinating side-effect of this version of the “written Seki rule” (which I think, nobody actually applies in practice, even professionals). I’ve seen it called “pseudo-seki”, so it is the name I use for the lack of a better name. I found it on the internet here: https://lifein19x19.com/viewtopic.php?f=45&t=3666&start=60.
The position is the following:
No prisoners, 5.5 Komi.
The black group in the upper right corner is involved in the possiblity of step ko: When completely surrounded, White could capture the corner stone, then if black cannot retake the ko, white can add the J7 stone to start a direct ko for the life of the black group. In the game however, white has one and only one ko threat at A5, and black also has one and only one ko threat at b (which is large enough: this will change later!), and thus white has no hope of winning the step ko during the game (since in the resulting direct ko, black will take first).
Furthermore, the black group is deemed alive by endgame hypothetical-play, with no need to add an extra defense move (capturing the white stone). This is because the existing ko is a step ko, so in hypothetical analysis, there are no ko threats, so white will take first, black will pass for the right to take the ko, white can only make the J7 move and then when black takes the ko, white can do nothing, so black wins the hypothetical play.
This is crucial because the game is very close: if black makes an additional defensive move like capturing the white stone so that there is no ko and his group is clearly alive, he loses by 0.5 points.
So, it looks like black should win by 0.5 points. However, white will argue that the top groups touch dame, and so are in seki! If they are counted as seki, white only loses 4 points of territory, but black losses 5 points (4 territory + the stone inside), and thus, white wins. So, to avoid this, black’s only hope is to fill dame, playing both triangle-marked intersections.
Note that, if white fills those, our analysis so far has been correct, the groups would not be in seki anymore, and black rightfully wins by 0.5 according to Japanese rules.
However, when black fills those dames, the situation changes, because filling them has made the black group larger. This means that, if white captures it, he will gain more points than before (2 more territories + 2 more prisoners). This makes black’s ko threat at b) no longer large enough: that means that if black fills the triangle-marked dames, then he loses because white will now start the ko, and will not answer black threat at b), effectively exchanging both corners, but now the difference is winning.
Thus, the seki rule makes this possition winning for white, if followed as written.
To the best of my knowledge, such a situation has never been actually claimed in a real professional game. My understanding is that in a real game, even professionals would deem the black group to be alive and not claim a seki instead, considering the written rule just “flawed”. Unfortunately I have no evidence for this, other than the lack of a counterexample (that would be: an actual pro game where a pseudoseki situation occurred and in which white won by claiming seki).