According to Reuters, the last body to amend the door would be Boeing themselves.
Spirit made blowout part but Boeing has key role
As part of the production process, Spirit builds fuselages for 737s and sends them by train with the special door assembly “semi-rigged,” one of the people said. “They are fitted but not completed," the person said.
At its Renton, Washington, plant, Boeing typically removes the pop-out, or non-functioning, door and uses the gap to load interiors. Then, the part is put back and the installation in completed. Finally, the hull is pressurized to 150% to make sure everything is working correctly, the person said.