I'm guessing that perhaps the USCG doesn't consider Grand Banks name boards/nav lights to be light screens? Their boats have to be approved by the USCG and the equivalent authorities in other countries where GBs are sold. Since GBs have been using this design of board since the mid-60s and selling their boats all over the world you'd a thunk that some authority would have said something by now if they had a problem with them.
Or it may well be like you said earlier and this particular rule is simply never enforced. In which case it's irrelevant what the rule says, right?