10 micron tolerance on body panels sounds like a typo. Coefficient of thermal expansion of steel is 6.5 microns/in/F. So, a 2 degrees F change in temperature will put parts over an inch out of spec. Imagine a 3 foot (36in) body panel going from a 80 degree stamping area to 75 degree assembly area. It will be out of spec by over 1000 microns!