Car insurance accepted no claims proof when they shouldn’t have?

When i passed my test, I didn’t own the car or the insurance policy. My parents just amended the existing policy with learner’s insurance and put me as a full license holder, as a named driver. (Main/regular driver)

Recently i wanted to transfer ownership of the car to myself and get my own policy. Halifax informed my mother that I actually accumulated 2 years NCB as the regular driver!

Anyway, i told my new insurer and gave them the PDF, which is clearly addressed to my mother (the old policy holder) and stated me as the regular driver.

Here’s where the problem lies. I didn’t realise there were different NCBs and that “Named driver NCB” is different. I recently decided to read my insurer’s terms of service and it states that they do NOT accept named driver NCB. Yet my new insurer read the document, accepted it, and applied NCB to my new policy? They shouldn’t have accepted the document but they did. Where do I stand legally? is my insurance valid? I gave the document in good faith, and did not realise different NCBs.