Given the timescale involved in international trade at the time there must have been some ship's at sea that thought they had a market for the slave's they were carrying.
Were slave's unilaterally freed or did the crew take them somewhere else?
Technically the importation of slaves to the US had been banned in 1808. The vast majority of new slaves in the US were children of other slaves. The slave trade still existed but enslaved Africans coming to the US would have usually had to do so via some indirect route (e.g. Cuba) or happened illegally. In short, there wasn't a stream of slave ships following to the US in the 1860s.