User blog comment:Paul Nebeling/An observation and a question/@comment-27384850-20170202154638

People have asked Kawahara about Argo, best we've ever gotten out of him is that she probably survived SAO. As for why she's nonexistent beyond Red-Nosed Reindeer, The Day Before, and Progressive, I'd wager it has to do with the time of writing.

The Day Before and Progressive naturally were written long after the story was completed in WN form. That only leaves the Red-Nosed Reindeer story, which I'd wager was written around the time the WN was coming to a close. If that's the case, then that would explain why we don't see her at any point after SAO, because she literally didn't exist when these events were written.

Naturally, I can't confirm this information, but we do know that the side stories in v2 and v8 were written later than intended for publishing (v2's stories were not written right after v1, likewise for v8) which is one of the big reasons I feel this way.