If you're the least bit unsure, replace 'em. I was enroute back to Kingsville Texas and one blew apart, replaced it with the spare...and sure enough 60 miles later the other one came apart (pictured ...
Tires were replaced "approx four years or so ago" from the previous owner. Well....I don't think that they were and judging from the outward appearance I had no reason to not believe him. Anyhow, yes it was the rear tires that came apart but I have five new 8 ply tires. I could not find LT tires when I needed them.