In Helena Ark the Union Army was taking the runaway slaves that came there and selling them to loyalist plantation owner along the Mississippi for cotton, which they then sold in the Helena Customs house.

Second of all, it depends upon whose definition that is used to claim that by 1864 slavery had already ended in Arkansas, Louisiana or any other southern state. Those regulations were passed by Union occupation governments and I would doubt the Confederate government of those same state considered those laws as valid.

Finally many southern Slaves were taken away, or run away, from their rightful owner and placed into public service of the United States army and other public works in violation of the laws of the United States and the United States Constitution. I say they were in violation because the owners did not recieve just compensation for those loses as directed under the 5th Amendment of that same Constitution. That was the law prior to the passage of the 13th Amendment. And that this violation of United States laws was not address even with the passage of the 13th Amendment.

Abraham Lincolns edict, called the Emancipation Proclaimation, did not superceed the United State Constitution, nor did it surplant federal laws. He did not have that power as President of the United States to superceed his own laws, although he regularly did. In other words Lincoln had no authority to free any slaves whether the people of any state was in "rebellion" or not.

If the slave owners were citizens of the United States, then they are due compensation for the property that they lost under the 5th Amendment. As you point out that some were in the North. And many southerners after the war did recieved payment for physical property such as timber that was cut down and used for military purposes as an example. Including Robert E. lee for the lost of his home Arlington.

But, if these same slave owners were NOT citizens of the United States then the United States Army was conducting a war against a soverign nation of peoples in the southern states which had the right to govern themselves as they pleased. And therefore the United States was the invaders and oppressors.

Too sum all of this up, until the passage of the 13th Amendment, under United States Constitution and Federals laws based upon Article 4, section 2, para 2, such as the Supreme Court rulings like Dred Scott, slaves were still property under United States law, the same as Arlington was for example.

Just because the law is ignored does not make it any less the law.