There are directory entries, which if they are genuine, (cropped from a page) that show Stanley Armour Dunham in Seattle 1956-1957.
Does residence on Mercer Island show up in that directory as living in Seattle? If so, and if the cropped pp from the directory are authentic, then the family lived there for that year at least. Or at least he lived there. One wonders why every bit of "evidence" practically is cropped.