system
Given the following post, respond as if you're commenting on Reddit:
human
[AWOIAF] Why doesn't Maester Yandel dedicate a single chapter of his work to the lands between Old Valyria and the Red Wastes?

Slavers Bay, Tolos, Lhazar, Qarth. None get much more than passing mention in relation to other lands.
gpt
He didn't have access to that information.

He never left the citadel, and the citadel had more books than he could read. So he assembled the information from the book he'd read, he knew of and subsequently read, or otherwise had access to and read.  Even some of the scrolls and books he'd read were incomplete, damaged, or otherwise lacked the information needed to form a complete, all encompassing encyclopedia of knowledge. 

He didn't, however, travel to witness these things first hand.