If you are the registered keeper of the vehicle and haven't received the NIP by now you're in the clear - so long as you have the balls (if necessary) to tell them it's been served too late.

If the vehicle is registered to someone else, so long as the feds issue the NIP to that person within the 14 days they can take as long as they like to get a new one to you, up until the offence times out at 6 months old.

If the RK does get one, and don't return it giving your details for the full 28 days they are allowed, that helps you get towards a time-out.