I drove through Farmington, from east to west, last year. I recall that the signs at the eastern end of what we map as Business US 64 through downtown identify that route as Business US 64, and the road carrying US 64 traffic around downtown to the south as Bypass US 64. Usually, where there is both a business and bypass US route, we treat the bypass as the mainline, unless like in Elizabeth City NC we have three routes through the city (business, unbannered mainline, and bypass) in which case the unbannered route is treated as the mainline.
Let's see what your photos show, especially at both junctions of the business and bypass routes.