Indeed, a matter for the court.
I came across a case a while back where the driver was alleged to have committed three offences, all in a London Borough which has a blanket 20mph restriction. He argued that he had only committed one offence but it was shown that he had stopped at traffic lights and generally been caught up in traffic between the offences. It was ruled he had committed three individual offences and got nine points.
Not so clear cut is where a driver exceeds the limit on a stretch of motorway which has a number of cameras. If he can show that he did not reduce his speed (to below the limit) between them he could successfully argue that he had committed one continuous offence. The downside of this of course is that he cannot use the "moment of inattention" mitigation and has to admit to tanking it for a prolonged period.
“…but if it stretches the entire journey then you're causing multiple moments of dangerous driving”
Excess speed alone does not generally support a charge of Dangerous Driving, spathi unless the speed is grossly excessive.
Sometimes when drivers receive multiple allegations a begging letter to the ticket office results in them being treated as a continuous offence, must more usually they prefer the courts to decide.