Macybaby

That last machine is probably not a National. Sears stopped buying from Davis long before National bought them out. Many, many companies sold to Sears with the badge of Minnesota on them. National may be one of the few that did not, as they had been supplying machines to Wards for a very, very long time.

After Davis, Sears used Domestic quite a bit, and White acquired Domestic and then started producing machines for Sears. The big change was when Sears started setting requirements for the machines, so those sold by Sears are not the same machine as the company made and sold elsewhere. (something Sears continues to do today)

This looks a lot like the one I have that was made by White, however it is very different than most whites, and takes a Singer style shuttle and needles (a requirement by Sears).
For a while, Sears had control of a company called King - and it could be that too.

This is the one made by White for Sears (though much later). It takes the same shuttle, needle and feet (side clamp) as Singer. However to keep so it would fit in other Sears cabinets, the belt is on the outside of the flywheel.