When the car was new and the popout was being replaced the nut would be removed, the popout replaced ,the coolant would not be drained, the nut would be tightened "good and tight", most of the Mechanics would not know what a torque wrench was let alone own one ,---even in the 70s i was laughed at for looking up torque specs and using a torque wrench to assemble an engine when the other workers were using an impact gun.
Replacing the popout paid 1.3 hour, replacing the headgasket paid 0.7 hour, rebuilding the engine including babbitting the mains paid 20 hours ---that even included taking it out of the car!!
Lowering the coolant lecel below the headgasket is prudent, just removing the 1 nut, torquing the 1 nut , then retorque all after running .
I work "flat rate" --but on Mercedes Benz, most jobs can be done properly in the flat rate time, many other cars have flat rate times that require "cheating".