Not only that but slaves weren’t freed in Confederate states or portions thereof under Union control on January 1st. The Emancipation Proclamation made that quite clear by listing the states/counties/parishes that it did not apply to.
Why? Because Lincoln had no power to free the slaves, who were legally owned property. He claimed the power as Commander-in-Chief to free slaves who might be employed by the Confederates as a war measure, just as intercepting private ships leaving Confederate ports.
Pennsylvania was the first state to gradually eliminate slavery, in 1780. By 1850, there were no slaves. Another guilt induced holiday for state workers.
As I said it was a POLITICAL document. It kept Europe out of the war, and they very much moving to involvement and doing so on the side of the south....
Once the EC was signed European involvement became impossible