i haven't read the light novels, or i might have missed something in the timeline, but would yosano and kouyou know each other? (obviously not a prerequisite for shipping at all lol i just got curious) since yosano left the port mafia when she was so young

I mean, this is not the answer I was going for initially, but after thinking about it for a while, very technically speaking they must be aware of each other's existence on canon basis. It's implied Yosano healed Kouyou when she was taken hostage by the ada: it's logic that she would have never allowed the ada to capture her unless she couldn't fight, yet she was doing fine once she woke up, meaning someone must have healed her up in the meantime– and the ada only has one doctor lol. Additionally, at the end of the cannibalism arc all the major ada and pm members were brought together in the same place, so according to these panels we can say for sure the two existed together in the same place at some point

I haven't read the vast majority of the novels either, but for what I know I think I can fairly confidently affirm they never interacted in any of them. Though you know, in the end it depends on what you mean by “knowing each other”: are they are aware of each other existence, yes; did they ever interact or ever even talk, eh, as far as we know, no.