Hola Julio
Chamberlain was promoted to full colonel in June of '63 and commanded the 20th Maine regiment, not a position for a brigadier general, which he was not yet. So no Chamberlain yet.
In June of '64 he was badly wounded during the siege of Petersburg while serving as brigade commander and was not expected to live. His corp commander Maj. Gen. Gouverneur K. Warren of the II Corp recommended his promotion to Brigadier General, which should take place before his dieing. Lt. Gen. Ulysses S. Grant gave him a field promotion upon this recommendation.
Chamberlain however recovered from his wounds and resumed his command again in November '64. Early in '65 he was given command of the 1st Brigade of the 1st Division of the V Corp, which would have been a highly honored and prestigious position, but from a game standpoint, not one that would merit it's own counter. Were a counter to be introduced depicting him, this would be the time to do it.