The rules are that they only get one go at issuing a PCN, and they have to get it right first time, so the good news is that you've won. They can't issue a revised PCN with the correct registration number because they messed up the first one, it's fatal to the PCN as Incandescent says.
The only fly in the ointment is that they might try it on anyway, either because they don't know this, or because they assume you don't know this. You'll probably hear nothing more about this as they will probably realise their mistake and give up when they try to get your address to send you an NTO, but there's an outside chance you'll have to jump through a few hoops to prove they messed up. My advice is to hang on to the PCN as it's your 'get out of jail free' card if they do try it on.