Even more June 19 was the day of a unlegal executive order call the emancipation proclamation, It also only free slave in land that the federal government and untied states had no control over. It would be like if said all Iran must have AC in there factory. It was not untill Dec 18 1865 over 2 years later that slave were free.
The Thirteenth Amendment (Amendment XIII) to the United States Constitution abolished slavery and involuntary servitude, except as punishment for a crime. The amendment was passed by Congress on January 31, 1865, and ratified by the required 27 of the then 36 states on December 6, 1865, and proclaimed on December 18. It was the first of the three Reconstruction Amendments adopted following the American Civil War.
Would make more sense to use DEC 18, than June 19.