I am 90% disabled through the VA, I qas medically retired in 2015 after 19 years of service. I applied for CRSC in April 2019 and recieved my approval letter of my CRSC pay at 80% dated back to Oct 1 2015 on Aug 26 2019. I received my first payment Oct 1 2019 am I entitled to back pay back to Oct 1 2015.