the Gunnar thing might be because you don't know his name and the book only records characters with names. (if this can be disproven that's my bad, but I can't exactly test this yet.) that should be why he showed up later because you found out his name is 0.47.5.EXTRA so he showed up, also on Garuik I believe he will show up eventually but he hasn't yet because he doesn't have any events to increase like with him so it doesn't need to be tracked yet, but since he is a guest character, he will eventually have an option for relations depending on how the guest writer writes him.
on Blake what do you mean "no heart"? I don't believe he has a heart event yet so he can't have one. also, Viccoria will prolly be someone you can date but that's a lot later since the game is currently focusing on male characters atm since that's the focus for romantic and sexual scenes and such at the moment. Hyao wrote on the main page it's focused on homosexual content but will not be limited to that, so if a woman character is in there, she should have a route eventually. like Rose. Julian though just doesn't have much stuff at the moment, but he will have a route eventually since he is in the book, any character in it will have a route eventually as I stated before it's just, they sometimes take a minute to show up in special cases, like Garuik isn't in it yet due to not having much in game yet and Gunnar you need his name before he's added.
also yes it does influence dialog because certain things when you speak with them change, like with Bernard when you have no hearts or any like he just casually greets you, but when you have 4 hearts and like max like he smiles and greets you more affectionately, however not every encountered character is recorded in there if you can interact with out of fights, like how Khalagor isn't in there yet after we fought we then fought him, and most merchants are just random merchants we just speak to and don't add to the book.