You need to write a statement to support your claim for each condition you are claiming. Whether it was diagnosed in the military may not matter completely. Example, if you know you went to the doctor while on active duty due to a consistent cough that would not go away or because of any other symptoms that could have been due to COPD, then state what those symptoms were. State what the doctor said. What medication was given to you. How long has it lasted and that you still have the problem now. For your knee and your back, state what you were doing when you first hurt your knee and your back. You were jumping on and off of trucks unloading equipment or supplies and you either hurt your knee and back or over time your knee and back began to hurt and it still continues to hurt now. Request an exam if they need further verification from a VA doctor. Make them understand that these disabilities exist and how exactly they began.