Scrabble, my oldest DD's favorite dog, is a Shep mix with a very dense coat. He's her running partner and happily runs 10+ miles a day with his best girl. You can see his ribs looking at him. Every vet we've had says Scrabs is perfect as is. He looks thin per the charts, but he's a runner and built like a runner now. His body burns off extra fat easily, and he's actually a very heavy dog at 93 lbs. Vets have told us every time, we call up and set up an appt for a Shep mix who is 93 lbs, they think we are going to walk in with a round fat dog, and we come in with this sleek running dog, who they think is 60 lbs until he gets on the scale.
To me, the charts are similar to BMI - maybe a good starting point - but if a person or dog is highly athletic, they are not going to work at all. DD14 is obese to the BMI charts, yet she wears a size 4 slacks, a 00 or 0 for tops.
These are working dogs, I'm going to assume they have the best medical care possible, because they are expensive to start with, and more expensive to train, so they want to keep the dog in tip top shape for as long as possible. So I really do figure that while the dogs look thin, they are in fine health and the vets know about the condition of the dogs.