I don’t think thats accurate.
Delaware is representative of it, they were a slave state, and they did not end slavery until all of the Confederacy was non slave.
“At the onset of the Civil War, Delaware was only nominally a slave state, and it remained in the Union. Delaware voted against secession on January 3, 1861. As the governor said, Delaware had been the first state to embrace the Union by ratifying the Constitution and would be the last to leave it. While most Delaware citizens who fought in the war served in the regiments of the state, some served in companies on the Confederate side in Maryland and Virginia Regiments. Delaware is notable for being the only slave state from which no Confederate regiments or militia groups were assembled. It did not free its slaves until forced to by the ratification of the Thirteenth Amendment to the Constitution in December 1865.”