Well here is my 2 cents worth on possibility.... There is a William Cook in Co B 6th Ark showing as captured at Helena who died in prison...now like Bryan said, at Helena the 39th Ark Inf, aka 6th Trans Miss Inf, was often referred to as the 6th Arkansas as well due to the name 6th Trans Miss and since COL Hawthorne was the colonel of THE original 6th Arkansas Infantry previously. I have seen many records on men in the Saline County company listing their regiment as the 6th Arkansas.... whether they meant that in connection with Hawthorne or as the 6th Trans Miss Inf I do not know but it does cause confusion for folks. So the William Cook (wish he had his middle initial there) listed as Co B 6th Arkansas may very well have been in Hawthorne/Cocke's 39th/6th TMI but the transcribers wrote what was recorded in the actual ledgers and documents. This William may have stated and referred to his unit as the 6th Arkansas to his captors when in reality it was Hawthorne/Cocke's regiment. If there was information showing when he enlisted etc it would have helped verify.