I can only assume they are the RK as that's who I've hired the car from.
It took me a while to get the NIP and I'm looking for grounds to appeal.
That is a very dangerous assumption. It's possible that the NIP you have is the 3rd or 4th in chain.
- First NIP to Finance company, they then name
- Hertz Corp, they then name
- The Hertz office that has the vehicle, they name
- The person who rented the vehicle at the time.
There is no appeal process with a NIP, you would have to take it to court if you claim the NIP was late. If you are found guilty the financial penalty will be many times larger than the fixed penalty you would have had a chance to accept.
Based on the non-evidence you have, I don't fancy your chances, so as Dirty Harry said, do you feel lucky, punk?