I doubt very many people actually change their tires after 5 years or 6-8, on a classic car that sees ~1000-1500 miles/year & sits in a garage or covered 90% of the time. 5k-8k miles and 60-70% tread remaining with no cracking or slipped belt issues does not warrant replacement IMO for the vast majority of people that own these types of cars going to dairy queen or car shows.
Not many people spend $800-1000+ on 4 tires every 5-8 years. Again, let me know when you are throwing away or actually paying a dollar or 2 each to have a shop dispose of 5-6 year old tires in good shape, I will take them!
Any age tire can blow out, have seen & heard of newer tires doing that too. Ive been a passenger in a car that blew a tire on the interstate back in the mid 1990's doing 60-65mph, was a junky mid 70's nova with rusty quarters/fenders... guy wasnt a car guy or experienced driver at all, it jerked the steering wheel some and got a little squirrely but no damage to the cars body nor was it ever close to losing control... every situation is different & everything you do in life has risks, changing out tires in good condition that are used at lower speeds every 5 years is not something I do or lose sleep over.
Another thing that applies here that nobody mentioned, just like many failures of engines or transmissions etc, is from... USER ERROR or negligence. Ive seen so many cars driving around with severely underinflated tires, or over inflated, or the owner didnt notice that their tire of any age is worn unevenly from bad alignment or worn shocks, had a bulge, etc etc, cant blame the tire for that. Same for engines, you cant really blame the engine itself for spinning a bearing because a guy put 2 gallons of ATF in the engine... or ran it off mt everest runnin shine! Point is there are way too many variables related to a tires condition or failure than some arbitrary date.
I check my tires inflation regularly as well as inspect them visibly and dont do things they arent designed to do, like 130 mph runs on city streets to test the max speed of the cam... or long high speed interstate use or racing on older tires.
I also know of one of the nicest lowest mile T/As out there (~5000 miles) thats actually driven that still has the original goodyear polysteel radials on it, guy drives it occasionally around town and to car shows etc, tires look like new still... so much for 5 years old, how about 45+ years?
Michelin makes/owns quite a few tire brands so their recommendation could be for more than 1 tire, they also own/make BFG tires now and BFG warrants them for 6 years, not sure if they suggest a maximum time limit though.