Compensation is available for the
journey.
If using a combination of tickets, it may be advantageous to claim compensation on all of them as one journey, or it may be advantageous to claim for just one or some of them. For examples, see my
York-Weymouth scenario.
If making multiple journeys with a single or return ticket, I would advise waiting until all journeys are complete before submitting a claim. If you were, for example, delayed by 30+ minutes into Nuneaton, then I'd explain what you did but the calculation would, I am sure, simply be 50% of the cost of your ticket. If you were delayed by 60+ mins into Nuneaton, then it becomes a bit trickier! On-time into Nuneaton and I'd expect them to pro-rata the compensation as far as Crewe.
There might be an argument to say that your
journey was Liverpool to Nuneaton, and you happened to break it at Crewe, but that may not affect the fact you were on time into Nuneaton, and therefore the journey wasn't delayed. I am not making that argument but I am just pointing out it could be made...
On the other hand, it is permitted to finish short on a ticket, so if your journey was to Crewe only, then that argument could be made that your journey was Liverpool - Crewe. Not applicable in your case of course as you are breaking and resuming the journey.
I also wouldn't advise claiming that you were starting/finishing short on a 'loophole' ticket e.g. the infamous Baldock to North Sheen via Elgin, or any other anomalous ticket, for various reasons. Again, not applicable in this particular case.