Hi Camaronut,
Sorry for the delay reply. I've been out of the country for a while.
Coker never got back to me even writing them twice. One last effort will be to call their phone number.
The tires are 6 years old so I figure the pro-rating wouldn't amount to much.
The other tires will be just as risky to drive, IMO. I live out in the country so driving at 55mph+ speeds on open side roads is common, and I don't trust the other 3 tires anymore as related to sudden sidewall failure. Also, this NTSB report from 2014 on sidewall failures vs. age still stays in my mind. Though this only reports on radial tires.
It's interesting reading.
https://www.ntsb.gov/news/events/Documents/2014_Tire_Safety_SYM_Panel_4b_Kane.pdf I'm looking at Diamond Back radial redline tires as a possible replacement. My show days for points are over so I just enjoy the occasional drive on nice days and having non-correct radials isn't an issue. Based on the recommend 6 year life of a tire as the report is suggestion, I can just buy the Coker tires again. But the price sure went up on them!
Mike