It's sometimes hard to define the term "Full Contact" in the Martial world, and in the sport fighting world, as I'm sure it means different things to different people and groups.
I remember the term first becoming known, at least in my world, in the late sixties from the Kyokushin guys led by Mas Oyama. If I remember correctly, it was both a competitive sport and the way they trained in their sparring. That being said, I don't think they were trying to knock each other out when they sparred, or even hurt each other (don't think that would make any sense) it was just a rule set, kind of like western boxing, with added techniques of course. It was a barehanded sparring, as was their competitions.
In 1974, the PKA (Professional Karate Association) was formed (again, we're talking about a sport here) where gloved hands and feet, rounds fighting with Karate techniques were utilized. The term "Full Contact Karate" was the most common way it was described. That's what everyone I knew called it. Two of the newly crowned champions of their first ever bouts (which were aired in prime time on network TV in the United States - a really big deal at the time) were Bill Wallace and Joe Lewis. Both have told me that when training for it, and continuing training in it, sparring was the same as every other kind of contact sparring - you weren't sparring like you were defending yourself in a street fight, you were just sparring with your sparring partners, as you would in boxing or any other contact fighting style.
As to Dan's OP, I don't think anyone is sparring on a regular basis going 100% to the head, or even to the body. Just doesn't make much sense. (Especially when you've learned to hit with technique). I'd be suspect of any trainer, coach or Sensei who allowed or encouraged people to try and take each others heads off. Not saying it's never happened, there are fools everywhere, but it's not the norm or good training. And it's not done by any professionals I know. And, besides the obvious safety factor - you just don't improve skills by trying to kill each other.