Ha! I bought those liter bottles, a lifetime supply of each oil. If they go bad in five years, my grand plan will sure have backfired! Assuming I survive that long myself! But I expect the oil will outlive that conservative guarantee and the actuarial tables give me good odds too!
May you live forever, Jim. (Actually, I think that's a Chinese curse! Sorry!)
About the oil, the makers just don't have data beyond five years. But oil has been in the ground for millennia, and the refining process just takes out some muck. It's the chemical additives, the ones that change in light, that may cause a little concern. My own opinion is that the base oil is probably good for anyone's lifetime, and the service is so light, and the change interval so short, that it will make zero difference. Anyway, your bulk purchases are in lightproof metal cans, aren't they? The problem doesn't apply to you, only to oil in plastic or glass bottles.
Andre Jute