Award from 2016 New ruling mobility

Hello, my son was recently sent a letter stating due to the new tribunal ruling on mental health and mobility the award had been looked at again and remained the same. Awarded high daily living and 4 for mobility. His condition is all to do with mental health. And can affect vision. I did not challenge this at the time. Can I send evidence from the gp( I think his letter was too late for the original decision) and can i send another specialist consultant letter who saw him prior to the original decision.
What I need to understand is can i send current evidence of his condition ( which he always had) or does it need to be from the dates during which the original decision was made?
Thank you

Thank You Gordon that is helpful, my thoughts are that I did not place too much emphasis on 'mobility award' because mental health was not awarded before the new law and so i did not appeal at the time . The review is based on the same. Do i go through the records and point them out. His medical records state agoraphobia and panic. How do I explain this and can the decision be taken to appeal and tribunal without risk of losing the award for daily living. Thank you

thank you for your reply
My son has a combination of conditions, he does go out. Sometimes he can not complete a journey because of opd. He would have to be picked up. Or guided back with somebody by his side. Other times he will not be able to leave the house at all for weeks He has OCD and vision disturbances.
This has affected him for more than 50% of the time
As there are a combination of issue it makes the situation difficult to explain
Please let me know if you can advise further on the matter
Thank you