By and large I already gave the deciding definition
As I said, you gave one of many that don't appear to have a common consensus or any authoritative source.
Edmunds - “Traditional 4WD systems
"Traditional" is the keyword there. Lots of AWD systems are driver-selectable.
Key to how a 4x4 works is a piece of equipment called a transfer case. This connects the vehicle's front and rear wheels, splitting the engine’s power evenly between them and making both axles turn at the same speed.”
The center diff does the same thing, which is why I said earlier that it could be considered a "transfer case", obviously with the addition of a differential.
And the article didn’t list the rules because it was wrong about everything.
Great, so we agree on that.
The rules are listed by the National Park Sevice
I edited my comment to include the NPS' definition and explained how and why it's incorrect.
Repeating yourself doesn’t make you more right. It does however increasingly make you look like an ignorant ass that has no desire to actually learn anything.