You only find out pretty far after the third light novel that other players are in Elder Tales as well.

Specifically the ones that died back when it was Sword Art Online. This includes Kirito(Shin)'s friends. Two of them were married in real life, and now have a half-elf, half-lord kid.

Except for some reason Asuna(Marino) has died a not-yet mentioned special death that means she won't be revived here. Probably. Maybe(?)

Also the dead Laughing Coffin members are back.

Also Shin's support characters (like PSO2 partner characters) now have real personalities, and have become incredibly famous. This is especially the case for Shunii Raizar, his first and best support character. The shop he owned is now super famous because she is the manager there, and she has been mediating problems and saving the world for the last 500 years. That's why she is incredibly influential, and if anybody knew who Shin actually was, he would be as well.

Oh, and you know that the church, the one that has been appearing since volume 1, is actually worshipping Rokuten? The six high humans? You didn't? It's because it's only mentioned far after volume 3.

Which brings me to my next point...