I've heard it suggested that we tend to exaggerate time here in Westeros and that there's likely only really been half as many Lord Commanders as we tend to think there were. Any ideas about this, fellow maesters?
According to Maester Yandel's World of Ice and Fire, the Wall and the Night's Watch were established 8,000 years before the Aegon the Conqueror's landing.
As such, 998 Lord Commanders of the Night's Watch is a plausible figure.