Sounds like a fair one. A mate of mine was supposed to submit a project to CGLI (or similar) to get an award, unfortunately, he was overcome by beer and women and omitted toIf it were me I would gently, but firmly approach with the, "Hey, I know I sent the change of keeper documentation in to you a lifetime ago and have just found out that apparently you did not update the system. Why am I still the registered keeper when I know I sent the paperwork to you".
As I recall there is no verification from them to you to inform you that they received the paperwork, and updated the system. So how were you supposed to know until it recently came to your attention through other means. Express your worry that you may be held liable for something that may involve the vehicle, etc, etc. especially as you have not been the legal keeper for 10 years.
It might be worth getting a lawyer to write a snotagram on your behalf. Do the AA, or RAC still have a drivers legal department?
Act confidently and decisively and watch as the adminsphere erupts into blamestorming.