I have a client who has a 1099-R from OPM Retirement Operations due to him being injured while serving overseas.  He is on disability retirement from the army because of this incident.  He is 45 years old.  Box 2a says "UNKNOWN".  Box 7 has code 3 for disability. 

Based on my research it appears that I leave box 2a blank as this is not taxable to him due to being injured while serving overseas.  Is that my correct understanding?