199 is correct with regard to the Bronze Star, and the difference between a 'Valor' award or a merit award.
Since your Father-in Law passed away, I believe you can write the National Personnel Record Center 9700 Page Bvd. St. Louis ,Mo. 63132-5200. You will need to know his full name, SSN, Army service #, Branch of service, or state veteran entered service. In this archive is where his Army Personnel records would be kept. Including awards and citations, as kin you are entitled to a copy of his records, I believe.
The National Archives in Suitland, MD., Vietnam Records Section would have things like After Action Reports and other avenues you could explore. Many Vietnam units have active web sights and if you know his unit and dates of 'in country service', you will most likely to find out what you are looking for. If he was a disabled veteran the organization that rep'ed him might have award letters as well. If you have any difficulty BC me.
GIB
199th LIB 66-67
187th AHC 67-68