Reference: http://www.angelfire.com/mb/lukegreatwar1917/Uniforms.html (excerpts)

Although this model came before the M1917 tunic, this tunic was used very often by the AEF. With the supply problems of the US Army needing so many uniforms so quickly, the surplus of uniforms available were used. M1912 tunics were manufactured in 1917 and even 1918.
Construction:

4 patch pockets, standing color where the collar discs were worn, interior fully lined, 2 slowly tapering epaulettes or shoulder tabs, Buttons with and without rims were both used on this model tunic.
Wool

The wool used in M1912's was generally a tightly woven wool and was khaki/tan in color.(the exact shades and color varied).
The last photo is of Sergeant Joyce Kilmer wearing an M1912 tunic. Joyce Kilmer (born as Alfred Joyce Kilmer; December 6, 1886 – July 30, 1918) was an American writer and poet mainly remembered for a short poem titled "Trees" (1913), which was published in the collection Trees and Other Poems in 1914. Though a prolific poet whose works celebrated the common beauty of the natural world as well as his Roman Catholic religious faith, Kilmer was also a journalist, literary critic, lecturer, and editor. While most of his works are largely unknown, a select few of his poems remain popular and are published frequently in anthologies.

At the time of his deployment to Europe during World War I, Kilmer was considered the leading American Roman Catholic poet and lecturer of his generation, whom critics often compared to British contemporaries G. K. Chesterton (1874–1936) and Hilaire Belloc (1870–1953).[2].27[3][4] He enlisted in the New York National Guard and was deployed to France with the 69th Infantry Regiment (the famous "Fighting 69th") in 1917. He was killed by a sniper's bullet at the Second Battle of the Marne in 1918 at the age of 31. He was married to Aline Murray, also an accomplished poet and author, with whom he had five children.