BB must be salivating at the fact that he got a 4th rd comp pick for Van Noy and now gets to bring him back
That's what the Patriots and the Ravens do. They plan in advance, so that if there are players who are going to be free agents, they decide whether they are going to be spenders or not in free agency. If they are going to spend, they try to trade their guys before their final season to get a pick, otherwise they get nothing as what they spend in free agency offsets the comp. pick.
Patriots knew Brady was leaving, so they opted not to spend to get the comp picks this draft.