At various times in this volume Mike talks about communicating with your dog. One of the comments I found very interesting. "With older dogs I like to take an informal delivery on the last retrieve. This becomes a cue that the test is over. If I take formal delivery it's a good sign there's more work to be done."
This quote is in the article Marking Mechanics on page 12, right column, next to last paragraph. Okay what is an informal delivery?
My guess is he simply takes the bird as the dog starts to come to heel rather than making come to heel and sit.