You're overthinking this. At a guess, this is connected to the fact that you are dealing with this on his behalf. If he's driving, pretend that he's a grown up and let him look after himself. I appreciate that modern things like the internet can be challenging for young adults, but think of it as developing life skills. And not playing chinese whsipers.
The case will have a unique reference number. If the COFP is accepted (including providing the identification details), the case will be closed. They don't go round at the end of the week trying to tally paid COFP receipts with offence dates.
If it does somehow slip through the net, he would have a defence of having already disposed of liability for the offence by accepting the COFP.
