Starting with the observation, I recently finished reading the four SAOP light novels and I realized something. They aren't narrative stories, but rather are memoirs, generally from Kirito's perspective.
To back up my claim, I noticed twice that Kirito refers to something that he had no knowledge of at the time these stories are occurring. The first one is a reference to Cardinal, but I filled that as "odd". The second one was the smoking gun.
While recounting the aftermath of the fifth floor boss fight, after the encounter with ALS, Asuna is upset. Kirito comments that "much, much, much later" Asuna told Kirito that she was afraid he was going to say something stupid. That's not the sort of statement that would be in a present time narrative, but would be quite fitting in a memoir.
Now for the question. Does anyone have any theories of what happened to Argo? She was alive on the day that Kirito and Asuna got married, yet doesn't show up for the SAO clearing party.