In the FWIW Dept., I've had OLD Federal plastic 20 ga. field loads that were loaded w/7/8's oz. of #6 shot start to split at the fold while still in the box. Yellow plastic 'high brass' hulls using the two piece plastic wads. Great ammunition too. Just used it in double guns where I could help manually guide it into the chamber w/those rounds that had started to expand toward the mouth due to the plastic cracking.
I expect they were made w/the assumption they would be fired within a couple of years of being manufactured. That wasn't the case w/all I'd bought. Me culpa, stuff happens. And it is more likely to if you wait long enough.
I've seen and purchased AA 28ga. skeet rounds that had the brass split in the box before firing. Two years back, now. I'm of the opinion that issue got resolved.
I've seen those longitudinal splits like you depict on some AAHS 12ga. hulls that were reloaded multiple times w/VERY hot bunker loads.
Just saying.
