I believe that in many cases the "excess headspace" bulges on cases are instead just oversize of even off center chambers. Mismatched bolts are likely a result of bolt-swapping by importers, dealers, or previous owners who didn't understand that what they were doing could alter headspace. When bolts were changed in service they normally (never say always) renumbered after lining through the number already stamped on it.
At least the Europeans were good enough to stamp numbers in lots of places on a rifle so there's less guesswork if the bolt matches. There's usually (never say never) no way to know if the bolt in a U.S. rifle that has seen several owners was properly fitted by an armorer using headspace gauges. When I was an ROTC cadet in the dark ages the arms room people took the bolts out of several hundred M1s for safety reasons and tossed them in a box without noting the number of the rifle they came from; first hand witness and not internet rumor.
