He can't.
By not paying and it transferring to sper the opportunity to challenge it has passed.
I spoke to SPER and they had sent notices to an address from when I lived in Qld back in 92. I also spoke to old main roads who also had me still living at the 92 address. So they asked for my NSW DL number and contact details so they could update my records as they noticed that I had transferred my DL to NSW in 92, but for some reason the system didn't update anyway.
They accepted that it should not have gotten to them (SPER) so sent it back to cops who had the options of forgetting it or issuing a new notice and they issued a new fine with 2018 as the date of issue and said that because they missed a new ticket / fine there is no statute of limitations.
I have asked for a court date due to time. I know it is the owner's responsibility to know who drives the car but after all that time it would be difficult but as a prison officer I kept records of every time I used my car and who used it, dates and places.
I was working and if the car was used for exports to hospitals and such and if so who was driving. So if they had sent me the fine anything unto 4 years ago I could have checked and if it was correct, pay it but if it was incorrect, I would be able to mount a proper defence.
Unfortunately I lost my logs and contemporaneous notebook in the Lismore flood last year. So I will be fighting this in court. It's only $100 and 1 point (that I never knew I lost and is now back on my licence) it's the principle of the thing.
If I'm in the wrong, I own up to it but they could issue anyone a fine backdated 5 years ago and not many people would be able to remember and would just pay it.