Whiskey River, I feel your post supports a theory I have had for many years:
Most of this age, age, age rhetoric is ****, ****, ****. After 10 years....replace them.
Your 9-year-old tire is still running but the 4-year-old ones failed.
IMHO a major brand tire, with no more than normal amount of weather-chccking
is still safer after 9 years than many of the new tires on the market today.
I would not hesitate one bit to run it until I could decide on replacements for all the tires on the rig.
Having retired after 40 years in the tire industry, I go back to the original introduction of radial tires in America. Goodyear hurriedly caught onto the bandwagon in the 60's after Michelin introduced the radial tire and the American public realized immediately it was far superior to the bias-ply tire.
Goodyear has ALWAYS come back with the same statement, possibly beginning with their first truck radial, UNISTEEL. "yeah, we had a few problems with that line, but we have taken care of all that in this UNISTEEL II." (you can plug in any of their lines in the proper place).
Can't tell you how many times over that 40 years I have heard that same basic story ! Goodyear has always had a fantastic marketing Dept.
"40 years in the tire industry; seen it all and done most of it"