I was a tire buster and then a mechanic for a Montgomery Ward’s Tire Center from 1975-1979. We featured Firestone Tires. You got everything right in your post. I do recall that someone would come in with tread separation and the tires were replaced with the same tire as part of the Firestone warranty. Sometimes the customer would return months later with tread separation in the replacement tire. My friend bought a set of 500s for his Gremlin even though I and the tire salesman told him that it was overkill for his car. When he sold the car 5 years later, the tire tread depth was almost the same as when I installed them because his car was so light.