I buy a lot through Sausagemaker.com, but I don't think they had the .com part until well into the 90s.
I can't recall using a prepackaged seasoning mix, except maybe once. I've been mixing my own spices for both ground and whole meat jerky for a looong time. Other than the basic brine, I don't have any standard recipe. When making ground meat jerky, I add the appropriate amount of curing salt, then spice it depending on the mood I'm in. My basic mix is just curing salt, pepper, garlic, and a dash of Allspice, along with some liquid smoke. As was mentioned, once the are strips ready for the dehydrator sprinkle some black pepper, garlic, or hot peppers on them.
I usually keep it simple, but sometimes get adventurous. Make small batches at a time until you figure out what seasoning combinations you like best.
I like making ground meat jerky because it's a little less work, and I can play with spices easier, but my preferred way is whole meat. Again, start with a basic brine of water, curing salt, and sugar. I add apple juice or lemon, soy sauce (careful not to make it too salty), and Worsteshire(?) sauce, along with garlic, pepper, and again, whatever spices I think will get the flavor I'm looking for. Most of the time I stick with the basic brine, with the pepper and garlic powder. And then dry it in the smoker.