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I read somewhere that the "standard" method for determining max psi was to find the psi where the tire blows off and then take half of that. So that would say that the blow-off psi is 204.
Seems like the most likely cause is a bead that wasn't quite in place. Maybe the tires were low at the start, allowing the bead to come out of place, then when pumped up it was just marginally attached, and after bringing it in, the increase in pressure was enough to blow it off.