Heritage Auctions of Dallas, Texas advertised a Confederate sack coat from the Western theater in about 2011. Its provenance is limited to an old label inside the coat inscribed, "Rebel Coat Captured by the Union Soldiers at Cumberland Gap." The Cumberland Gap sack coat exhibits some early characteristics that include a six-button front, and a six-piece body. The collar is two-piece, inside and out. These characteristics were later usually simplified to a four-button front and four-piece body. Otherwise, the one piece sleeves, exterior breast pocket, and length are typical of Confederate sack coats. The bottom edge is well above the cuff line.
The provenance, such as it is, suggests that this is a Western depot coat. Last of all, the coat retains at least three of its buttons: all of which appear to be wooden, two-hole buttons.
Images courtesy of the Heritage Auctions.