Bolt Elongation

This is why I much prefer beam-type torque wrenches, or ones with the digital readout that beep. You can watch the torque increase as you tighten the fastener so you know exactly where it is (not super precise of course depending on how the scale is printed) but you don't have to depend entirely on the internal spring in a clicker-type to give you the right torque. Although I agree with others that bolt was likely over-torqued at some point in its life.