GRRM does love his unreliable narrators. Jon and Sam have an interesting conversation about how many Lord Commanders there were before him, and there's a few fan theories spun off out of that. And A World of Ice and Fire is a "historical" document written by an in-universe character who presents the history through his own biases.

I'd be interested in speculations on the impact of an off timeline. Surely it affects the "mundane" very little - most people likely do not care about anyone outside living memory (probably a couple hundred years, since a lot of time is reckoned from genealogy).