UC WCA mandatory reconsideration or new assessment?

I am appointee for my son. We did an ESA credits only claim at the start of the year, which we were told he had been placed into the support group, so we claimed UC when he finished his foundation degree. It has since come to light that we were wrongly told he had been placed into the support group, so he only gets LCW on his UC claim. He has now started a new university course, and needs his UC to help him afford to live in university halls (his room alone is nearly all his maintenance loan due to being an accessible studio that he needs due to his disabilities). I have been told that I can ask for a mandatory reconsideration even after the one month cut-off, and have a copy of the assessment report. The jobcentre have also sent out a wca50 form to complete another assessment. At present his maintenance loan wipes out his UC payment, but should he get the either LCWRA element he would get a small amount and would get enough to live on during the summer holidays.

So, should I give up on the MR of the old assessment and just complete the new form, or do I just go for MR and ignore the new form, or both??