1.The nature of my absence is different - Frequently absent abroad vs Permanently resident abroad
An even more important reason why you should have ensured that any correspondence relating to the vehicle would be properly and promptly handled (with the most reliable way of doing that being to change the Registered Keeper).
2.It was sent to their address vs my father's former address,…
The police have only one address to correspond with – that of the Registered Keeper - as maintained by him. They have no duty to send reminders or try to trace the RK if they do not receive a response. The principle being questioned in
“Whiteside” was whether a notice sent to that address could be deemed “served” (and so satisfy the requirements of s172) even if it had not actually been seen by the intended recipient. The court ruled it could.
3.It was their vehicle and they were responsible for it…
But you were the Registered Keeper and as I said, you cannot delegate the Registered Keeper’s responsibilities.
4.I was unaware I was still the registered keeper and I was unaware of the status of the car…
That is entirely your fault. One of your responsibilities as RK is to ensure the DVLA records are changed when you are no longer the keeper of the vehicle (if appropriate, which in my view it was in your circumstances).
5. Upon discovery, I took positive, demonstrable steps…
But far too late.
The conclusion you seemed to have arrived at is that in your situation any number of offences could have been committed by a person driving a vehicle of which you were the registered keeper and no action could be taken against them (because the police did not know who they were) or you (because you had left the country). It doesn’t work like that.
Case law establishes principles, not rules which can be applied in every set of circumstances. I have little doubt that a court hearing your defence will be directed to
"Whiteside" and asked to rule that the principles in that case apply to yours.
The options for you (if an approach to the police fails, as I imagine it will) are:
To either plead guilty (a fine of one week’s net income, a surcharge of 40% of that fine, £90 costs and six points). Or…
To plead not guilty and face a trial. The outcome in that case if you are convicted will be a fine of 1.5 weeks’ net income, the same 40% surcharge, around £650 costs and six points. Or, of course, nothing at all if you are acquitted.
Bear in mind that pleading not guilty and facing a trial will require your attendance in court (unless the court agrees to you sending a legally qualified representative, who you will have to pay for).