On other hand, it might all be in the spelling of the surname:
Buchanon, R.T. TN 50th Inf. Co.B
Buchanon, Robert TN 19th (Biffle's) Cav. Co.A Buchanan, R. TN 3rd (Clack's) Inf. Co.E Buchanan, Robert TN 4th (McLemore's) Cav. Co.F