In the British "Television" magazine; formerly "Practical Television", only a few years ago the loose screw topic was discussed. When a set was brought in for repair and the (UK 13A) plug was checked for correct fuse and wiring it was often found the neutral screw was loose. Sometimes loose enough to prevent connection. The mystery was never officially solved; the closest plausible explanation was that the neutral pin was free to move about as the plug was inserted and withdrawn from the socket. The live pin wasn't as it was riveted to the fuse holder and therefore mechanically isolated.
When I moved into my house I checked every switch and GPO and found the neutral screw in one of the kitchen GPO's had never been tightened but the fibreglass insulation in the wall had kept the wire pressed in.
