The person that changed my tire said that a belt had slipped. It was destroyed. As for the dates, my new tires are 2014 per the DOT code. The old ones were probably original to the rv which is a 2009 Winnebago Class A. It had about 33,000 miles on it at the time of purchase.
It is a good thing that the blown tire was one of my back, tandem tires. When I inspected the tire at the purchase of my RV and later, when the tire store looked at them before my trip, the sidewalls looked fine. I should have known better.