Most awards of the Medal of Honor for the Civil War were made long after the war ended. Veterans and veterans groups lobbied for recognition. At the head of the line were politicians and those who had stayed in the Army. Posthumous awards were quite rare, in line with the customs of the day.
After events of the Spanish American War, the Boxer Rebellion, and other turn of the century conflicts, standards were tightened and the Medal of Honor became the prestigious award that we know today. That is, until the White House started using it as yet another tool in their political correctness partisan behavior.
“...This board rescinded the awards of 911 Medals of Honor. Stricken were the 27th Maine, the 29 officers and men who had accompanied the remains of President Lincoln from Washington to Springfield, Illinois in April, 1865, Dr. Mary Edwards Walker, and another very colorful hero of the Indian Wars, William F. “Wild Bill” Cody. Cody, like James J. Andrews, had been a civilian guide or scout and thus was not eligible for the award. The most ridiculous award that was rescinded was one that had been issued to a Lieutenant Colonel Gardiner in 1872 by Secretary of War Belknap upon Gardiner’s application. Gardiner wrote, “I understand there are a number of bronze medals for distribution to soldiers of the late War, and request I be allowed one as a souvenir of memorable times past.”
With this action in 1916, the total awarded for the Civil War came to 1,520 of which 1,196 were Army, 307 Navy, and 17 Marines...”
http://www.andrewsraid.com/m_review.html
When did Chamberlain receive his for Little Round Top? It was years and years later, iirc.