Some of the earlier ('80s) P226 had a slightly thinner frame. It failed the AX-crush test where an ax was dropped onto the triggerguard to see whether it would crush the guard (and thereby disable the trigger). Afterwards, Sig widened the frame slightly and the modification allowed the gun to pass. This is why some of the earlier aftermarket grips won't fit the later guns. The aftermarket folks weren't aware of the dimensional changes and continued to make grips for the narrower frame.
I've only seen one Sig P226 with a cracked frame. The crack was along the rail and for the length of the rail. I suspect the owner was using subgun ammo but he wouldn't fess up. We were also waiting to hear from Sig their analysis of what happened.