PIP & car tax what they don't tell you

I used to get free car tax with DLA because of High Rate Mobility and car was in Disabled Class for taxation. After being transferred to PIP I lost the High Rate(enhanced) rate as i was given 10 points and need 12 for this. My award letter for PIP told me I had a week to get my car taxed as it would be cancelled and even my insurance would be invalid. I went off and taxed the car for 6months. What the PIP award letter did not tell me and I have found out since is that if you have standard rate 8points(i think) you are entitled to a 50% reduction in road tax. Why doesn't the PIP award letter state this ? because I suspect they don't want everyone to know and want folks to tax at full rate.
i have spoken to DVLA and have to send them 1. PIP award letter.2.V5C vehicle reg cert for taxation class to be changed to 50% 3. V10 application for tax form. 4. Cert of ins. 5.MOT . 6. Cheque for 50% of car tax. I am told I will be given a refund for what remains that i have paid.
What is really worrying is that the award PIP letter only gave me a week to tax or insurance would be invalid,what if I was away on holiday driving around unaware doesn't bear thinking about,who are these people making these things law? Flawed or what. I feel a letter to my MP coming on.