I have had my say elsewhere about these matters so won't duplicate that here, except to repeat that I assume we can all agree that without measuring each bolt head to see if it was within specs for its size number, the process becomes somewhat random and arbitrary?

As I have access to about 50 stripped, clean and well-used bodies I shall have a look at the rear lugs to see if I can see any signs of extrusion of the metal.

I'm also not seeing any reference to the hardness or hardening of the lugs on the bolt itself; where these not hardened to the same extent as the lugs in the body?