I think that the rating system of heroes in One Punch Man has an error, what I understood from the anime is that if someone reaches Top 1 in some X-class he will have the option to get into the next class. but if that is true then if this guy agreed, the guy who was in the Top 2 will be now in the Top 1, and he will have the option to switch to the next class as well, and this thing will happen until this X-class run out of heroes, but apparently, this thing didn't happen in the anime.
so is this just some mistake that the author didn't notice or there is something that I'm lacking?