There may be a general belief. It's not true though. Ask any police constable. Using common sense and discretion is an every day part of the job. In the case of displaying your boat name (or your paper licence for that matter), what would be the point of prosecuting? If the checker can see the index number and check that it's licenced, their job is done. Why would anyone want to add complication to that?
Roving winter permits are a very different matter though. They came across like a protection racket: "pay up and we'll leave you alone".
Having said that I've alway been puzzled by CRT winter moorings generally. To my mind they walk the tightrope of what is said in the 1995 Waterways Act, specifically in regards to the phrase "The Board are satisfied that a mooring or other place where the vessel can reasonably be kept and may lawfully be left". Essentially, CRT grant a winter mooring, thereby providing a short term place for the vessel to be kept". This is CRT acting as poacher and gamekeeper and doesn't sit easily with the intention of the legislation.