Even without a date, a few specific years of the Buff can be identified from design changes:
1913 PDS Type I, from the reverse design
1921 PS, from the ribbons and knot redesign
1923 PS, from the left ribbon redesign
1925 PDS, from the left ribbon redesign
1931 S, from the left ribbon redesign
Your coin could have been narrowed to three years (1913-1915) based on the Type II reverse, ribbon design, and weak LIBERTY.