When you buy a used car or truck and the tires seem fine you don't run out and check date codes or just change out the tires just because they're used.
If you buy nos tires with a date code of 5 years or less I honestly see no issue at all. When you consider that you can purchase an nos set of tires already mounted on 24 bolt wheels for must less than the cost of just new loose tires I don't get the debate. The cost to mount them is far from inexpensive.
My nos MTRs were five years old when I purchased them and I have now had the truck over five years. The tires still look new with zero cracking. I know the main issue as tires get older is they get harder and a tad rougher but still fine in my eyes for the old girl. It's an old military truck not a new corvette.
Sorry for the rant. Just my .02 cents.
Mark
First of all, I would definitely check tire date codes if buying a used car, especially if it's a low miles car more than a few years old. I learned that lesson the hard way buying a chevy caprice back in the day that had 4 new-looking michelins on it (it was actually a selling point in my mind, no cracking and full tread). I bought it from a retired couple that never put any miles on it and the tires were aged out. Wife had a blow out and I figured it was just bad luck. Wife had second blow out, checked date codes and the tires were like 11 years old (I was young and foolish not checking dates after the first blowout). Thank goodness nobody was hurt, but not a happy wife and lesson learned after putting 4 new tires on it.
I think new vs. used really depends on how you use your hmmwv. Mine isn't a daily driver and I might average 2000 miles a year on it (only 1600 this last year I've had it). I actually drive it 2-3 times per week, just lots of short trips. So, I figure my tires will likely age out before they wear out (maybe). Even stored in a garage most of the time, 10 years is about the max I'm gonna be comfortable before replacing them. I paid a little under $500/tire for my new Enforcers, so I figure $50/year per tire and I don't need to mess with remounting them for 10 years. If I buy a 2018 date code tire, I only have 6 years of life remaining, so it needs to cost at least 40% less than a new tire and then I'll be remounting them in 6 years. Remounting 4 tires with run flats is a pain in the butt and would take me at least a day, probably a weekend at the pace I move (and I'd be buying new o-rings, etc.). No right or wrong answers here, I'd absolutely consider used tires from a good source if I was putting 10k miles a year on my truck.