Carlisle tires

I replaced the original Tow Max tires on our trailer in late 2010 with Carlisle ST's. (I wanted to go to LT's but the decreased distance between the tires would have been too narrow to use my chocks.) Over the next two years I experienced 3 goose eggs on the sidewalls. I'm pretty conscientious about tire pressures and check my tires at each rest/fuel stop. No complete failures or blowouts. My dealer replaced them with a very reasonable adjustment. I've not had any problems in the last 2-3 years with any of the replacements, nor the remaining original. After reading some of the posts here, I wonder if I didn't get some of those "early" tires and the replacements were of the improved model. We're presently wintering in Texas and the tires are under wheel covers so I'm not going to verify that. Maybe next spring....