The USA flag on the reverse has 38 stars so it is clearly post ACW. Since the 38-star flag was superseded in 1889 we could assume that the flag was at least ten years old during the Span Am war. Although there are no guarantees that the manufacturers of this flag got the number of stars correct, there's no reason to believe that they would show anything other than the then-current USA flag in amongst the banners of the CSA.