Well, in THK, Dunk knows his heraldry: “Though he had never learned the magic of reading or writing, the old man had been relentless when it came to teaching him heraldry, often drilling him as they rode.” Now Egg knows it better, hence “He was not japing me when he said he knew every good knight in the Seven Kingdoms, Dunk thought ruefully.”
But I think Arlan might have skipped the Peakes out of the whole Redgrass thing. Also, things you learn by rote are really quick to fade, and by TMK it’s been a couple years.