[Note: This is an excerpt from a mail concerning a recent addition to the heraldry files. For the arms of the Freys, please look at the Heraldry section of the Citadel.]
One thing, though -- you gave us the quarterings for all save the two Rivers' with the Frey arms by the mother's arms. However, as I was about to start work, it struck me that at Winterfell the two Walders actually quartered their arms by those of their mothers and their grandmothers . . .
This of course makes me wonder whether Ser Cleos's arms should be the same -- quartered by Lannister and Royce. However, I suppose it wouldn't be inappropriate at all if Ser Cleos and the rest of Ser Emmon's brood preferred to keep the lion alone with the castle, since being the son of a daughter of a Great House is a pretty major "achievement."
Yes, I agree. Quartering is still not the usual practice in the Seven Kingdoms. It did not really become standard in real life until after knights had stopped carrying shields in battle, and for good reason -- the sort of grand quartered coats that later became common would have been really useless on a battlefield for purposes of indentification. Much too confusing to the eye. Since they still carry shields in Westeros, I think quartering is as far as they go... and even that is more the exception than the rule.