Wow . . . I am now on split #3, and have exhausted all of my spares . . . I guess I start the hunt again.
Wow!
I'd have to sat that either you got a bad batch, or you live under a leak in the Ozone layer, or your nosy neighbor who hates MVs is cutting your tires!!
I think I'd get the next set from a different vendor/source. I'd guess that these weren't stored properly prior to you getting them!
I have a '52 GMC Deuce with VERY OLD tires on it. The fronts have huge cracks, but they STILL somehow manage to hold air!! That said, I wouldn't trust them further than I can push the truck (i.e. not far), and a new set of NDTs is on "the list". Holding air is a minimal requirement, but for tires to be safe the rubber needs to be pliable & the interior structure needs to be strong. I've seen tires that looked like new fail, so I'd never trust tires that are showing signs of age (or that are simply OLD!) on the street/highway. BUT off-road at low speeds I'm more likely to use an older tire IF it looks structurally sound.
I hope you have better luck with your next set!
(& keep an eye on that nosey neighbor!!)
-Bear-