2000 PORSCHE 911 Tires Problems

Driving gently at 50mph down a smooth road the tire suddenly deflated; I pulled over to swap it out for the spare. On examination of the tire the inner side wall delaminated in 2 places, I could find no reason for the failure. There are no screws or nails or other damage that would explain why it deflated other than the sidewall delaminating. The car had an oil change 4 days before the tire incident and the tire was examined and found to be at the correct pressure. The rubber around the failures seems soft and tears easily. I have a matching set of these tires on my car, same brand and type. I did some searching and found a recall on this brand tire which describes exactly the failure I experienced; when I called the manufacturer they told me my tire does not fall under the recall.