Lot number doesn't change from order to order. So all they currently have in store right now is the same lot number. Lot number will change when all they have now is depleted and they receive a new order. So you can stack it deep, and if you have enough for the rest of your life, consider that you'll never have to work up a load. If you shoot campros in an AR (in other words, if you're not worried about accuracy like with a bolt gun), you can work a load without a chrony: make a load 10% lower than the IMR4064 load data, and increase the load until the AR cycles correctly all the time.
4064 is roughly the same as varget but a bit less stable in temperature and the kernels are a bit bigger than varget. For the same price I would choose varget, but for 26$/lb instead of 40$/lb, the choice is easy.