My Grandson has been listed on MEB for 3 years. Now all of a sudden they called him in to sign MEB paperwork. I'm helping hime with MEB I told him not to sign. USAF pitched big time fit but since have settled down. Refused to give him copy of MEB. Pressure caused them to appoint new PEBLO. Waiting to see if they have taken C&P Exams off. When we started he had Traumatic Brain Injury as well as 10 more. Now according to old PEBLO only has knee injuryIt is always an option....however, the Impartial Review is an activity within the MEB process, so really, what you are looking for is challenging a finding of the MEB. Since the MEB cannot change or overrule the VA, there is little sense in trying to use the Impartial Review to address the VA's actions.
For the type of error you are describing, it is often difficult to get a change....(though, I have seen rare cases where requesting assistance through the VA and or MSC have worked to get an addendum or new exam). Most times, the erroneous VA exam would result in an erroneous rating (but, of course, if the rating is right, then no problem) which would have to be addressed with a one time VA Rating Reconsideration Request (VARR).
I gave a bit of a longer answer...summed up, Impartial Review is not route to address problem you are describing. Procedurally, would be the VARR.