Keith, you made out like a bandit on the deal. Congratulations!
The wads I had go bad were not notable in any other way. I have all my wads, in their original bags, on shelves where I reload. I probably have 25 bags of various makes and gauges. I was about to reload some shells, some years ago, and when I got down the wads I wanted and began to handle some of them I noticed the petals would just break off at the base. They had become brittle, having lost all pliability.
Wish I knew more about what contributes to this. All I can add is that most of the time my reloading premises is not heated or air conditioned, and there are no windows for direct sunlight to contact them. It's been years since I had that issue with those wads and I've never seen it recur. Because of that I lean towards thinking there may have been a difference in the composition of the plastic in a certain lot, that led to the deterioration.