WSS is wrong translation for English. Thats what I said, you don't say strongest marksman, you say greatest marksman, same for swordsmanship.
So Dai Kengou is the first title they used in the manga, there aren't 3 different titles, all 3 are the same title. They never even once said someone said ''I am dai kengou and also saiko kenshi also sekai ichi no kengo'', they also say ''sekai ichi no kengo'' as well, again same WGS title, there aren't 3 different titles, its the same title with different names. Grandmaster swordsman = greatest swordsman, and when they say saiko no kenshi, it also mean greatest swordsman, because in English you say greatest not strongest for proficients like marksmanship or swordsmanship.