I guess it depends on what you define as “the North.”
In 1860 the term generally meant the free states, in which there were no slaves, so I fail to see how the South could get slaves from them.
Well I guess that answered itself then.
The South would have to have kept all the slaves in the South if they had taken the bait.
Just a back door way of making sure all the slaves didn’t end up in the North to live.
I don’t know how they were treated up North at that time.