There were about 4 million black people in the US in 1860, about 10% of which were already free. By June 19, 1865, most of the slaves had learned of the end of the war and that they were no longer required to work for their former owners. Word got to Texas late but maybe a few hundred black people in Galveston learned about the end of the war on June 19, 1865, so to make that the grand celebration of freedom seems to be making a mountain out of a molehill.
Once Lee surrendered on April 9, 1865, Southern whites appear to have recognized that the game was up (Jefferson Davis excepted). I read of a lawsuit once concerning someone in Mississippi who had learned of Lee's surrender before anyone else in that locality and went to spend his Confederate money right away. He was found guilty of fraud--the storekeeper would not have accepted the money if he had known about Lee's surrender.
It was ratified on December 6, but it appears it wasn’t implemented for a few weeks.