How long does beef jerky last in an unopened package? How about an opened one?
An opened one - not very long. Oxygen starts eating at it really quickly, which is why there are Oxygen absorbers included in every packet - those absorbers are just there to counteract the factory-sealed oxygen and the small amount that seeps in through the not-perfect seal, but they will be overwhelmed when the package is opened. I’ve kept some half-eaten large pouches around for a bit, but they maybe will be good for a week. I quickly switched to buying the large bag of pouches rather than one large pouch.
A sealed packet should be good for years if not decades. I have a bag of pouches I bought at least 5 if not 10 years ago that I occasionally (a couple times a year) take a pouch out of to eat in place of my usual breakfast meat when I forget to defrost it, and it’s perfectly fine.
So what’s the difference, then, between modern jerky and what our ancestors made? The whole point of making meat into jerky is (or at least was) to preserve it.
Typically it was more salted and more dried than contemporary commercial jerky. And its users probably weren’t too concerned with it being stale either.
I had beef jerky mold. Pretty gross.
Probably depends on where you live, too. I’m in a hot humid climate - EVERYTHING goes bad quickly at room temp. Or at least it lumps up - salt doesn’t go bad, but it turns into a rock, as does sugar. (I fight back with tons of 50gm food-grade desiccant packs; those work pretty well.)
Wooden kitchen tools get moldy, for that matter. I used to store them in the freezer, but that was awkward so I Googled and found an alternative - soak them in food-grade mineral oil. Much better.
Anyway, I’m pretty sure your jerky would be gross within 3-4 days here in East Hawai’i, unless you stored it in the fridge.
Dog jerky treats last much longer
Hey they smell good. And the dog eats them. With out compunction.
Dried meat historically has often been something you simply couldn’t chew, unlike the relatively soft jerky we love to snack on. In the past, it was more like wood - you’d either have to soak it for a while, break off a piece (probably not with your teeth, though, for fear of damage to them) and suck on it for hours until your saliva softened, or smash it into pieces and put it into a soup or stew.
It was a lot more dry and a lot more salted.
And it still could go bad in warm, humid environments. As @CairoCarol points out.
I double-clutched on this. “Who makes jerky out of dog meat?” 
The light came on after about a second. “Jerky treats for dogs”, not “jerky treats made from dog.”
And you’re right. Pet treats can be disturbingly palatable-smelling.
Pretty good bet it’s commonly available in those countries that routinely eat dogs. Of which there are several.
Ah, remember those hamburger shaped dog food…?
Smelled so good.
no! I never took a bite, not on my diet
Allow me to reassure you about baby oil.
Yeah, the snack stuff sold in stores isn’t real jerky, I occasionally buy the real thing from a local butcher’s shop that sells it. Bone dry enough to literally snap like a stick, you put a small piece in your mouth and gently work it for about five minutes before it can actually be chewed.
I freeze jerky for the kids.
The grandwrex love meat popsicles.
And the dogs love them when they have them.
It’s all for family unity.
Ganes Burgers
I didn’t think this was a real term. I just thought it was a funny line from The Fifth Element.
I thought I made that up. 
Gaines-Burgers
They are still around. Sort of. Now with Chia seeds! https://gainesburgers.com/
I loves me some chia seeds.
Oh, lord. I didn’t think what I just thought. Did I ?
(Oh, man they’re not fake red anymore)
What about making pemmican instead?
For long lasting meat, canning is probably the way to go. A lot of the best-by dates are five years after manufacture and would probably remain ok for quite a wile after that. Canned ham, roast/corned beef, tuna, chicken.