I did some more study....
The Emancipation Proclamation was signed on September 22, 1862. That’s a Historic Event!!
From Wikipedia:
Although Juneteenth is commonly thought of as celebrating the end of slavery in the United States, it was still legal and practiced in Union border states until December 6, 1865, when ratification of the Thirteenth Amendment to the Constitution abolished non-penal slavery nationwide.
Let THAT be the National Holiday.
In practical terms liberation was very spread out. Some slaves had fled to Union lines and were effectively free even if not legally so before this, and then after Jan. 1, 1863, as the Union gradually gained control of more and more of the Confederacy, the slaves there were told that they were free.
How much practical difference it made may have varied--probably some continued to work for their former masters because that was the only way they would have food to eat. A lot of the house servants seem to have remained with their former owner's household even later (reflected in Gone with the Wind.) Former President Andrew Johnson's best friend in his post-Presidential days was one of his former slaves who continued to live with the family.
I was told by a great-aunt (born on the day that Jefferson Davis died in 1889) that at end of the war former slaves begged to be allowed to stay. I wouldn't be surprised if that sometimes happened--they had no money to buy land for themselves and they needed some way to make a living. The difference was that they were free to leave. (My great-aunt's father was a 14-year-old boy in Virginia at the end of the war--I don't think his family owned any slaves.)