I think I read that of all the global events of the MGB SC cracking, this same airframe had one in 2006 which was discovered on a post-maintenance ground run where the engrs found a leak.
The revised flight envelope had already been put in place at that time and the aircraft will have been operated within those limits. Prior to that time, the main flying exercise being taught that exceeded Bell's recommended pitch & roll flight envelope was wingovers which was removed from the Griffin syllabus as soon as the new operating limits were known.