The Official Count of Kings

[Lord Varys]

3 hours ago, Syl of Syl said:

The fact that it shows up in FaB in the same form, kind of makes it Gyldayn's list tho, doesn't it. That's semi-in-universe.

Family trees and appendices are not part of the narrative framework of the books. And even if it was - the appendix of AGoT definitely wasn't written by Gyldayn.

2 hours ago, Vaith said:

Since a lot of this argument seems to be coming down to whether Rhaenyra is counted or not, I am going to go with my personal theory that the rather Green Hightowers, as Defenders of the Citadel, made sure that Aegon II's request to remove all references to Rhaenyra as queen was fulfilled for quite some time until it became tradition. 

It turns out that Aegon II never made such a request, though. His decree that Rhaenyra never was a queen didn't find its way into FaB - despite the fact that people did point out to George that this was missing - which means it is no longer part of the canon material (the incomplete novella versions have been superseded by FaB).

However, it seems very unlikely that maesters have to deal with official demands of kings and lords as to who they can count as a monarch in historical texts.