When I buy kyosho rubber, I buy bulk from the cheapest source. Bonsai hobby was my last recent purchase where I bought 10 packs of k20 radials for the rear, 4 packs 30 slick front, 2 pack 30 radial front, and 2 pack 40 radial front. The kyosho tires not losing performance in or out of the bag, means that these could be good for years. My last race I used tires that were opened and mounted 10 years ago.
PN tires I almost exclusively get from kenon. It's the only way to really know that you have the newest rubber.
when I mount tires, I label the wheel with the type of tire and sometimes date them. This makes it much easier when going through different pre mounted tires on race day to dial in front end traction.