“Retroactive Pay” OR “back pay” OR “retro pay” “Fort McClellan” “future exams” Tinnitus “Convalescent Ratings” TBI OR “traumatic brain injury” OR “traumatic brain inj” “Compensation and Pension Exams” OR “c and p exams” OR “c & p exam” OR c&p exam” “tdiu” OR “iu” OR “unemployability”