You are correct that Fletcher did not become governor until 1865. It may be that Lewis was appointed as an aide to Fletcher related to the new militia organization Fletcher set up. There are two OR letters from Gen. Fisk to Col. B. W. Lewis at serial 101, p. 1305 and serial 102, p 0873, but in correspondence of 1864 in the OR, Lewis does not use the title Colonel. Neither of the 1865 letters indicate that Lewis was Col. of a particular regiment.

Tom Jones