[okie01]

So the flags of those ships are irrelevant, since they were all outlaws.

And, in any event these flags would not have resembled the Confederate battle flag -- which didn't come into existence until 1861 (or 2).

I.e., it never flew over any slave ship.

[BroJoeK]

okie01: "And, in any event these flags would not have resembled the Confederate battle flag -- which didn't come into existence until 1861 (or 2).
I.e., it never flew over any slave ship."

Agreed, no dispute about that.
The second Confederate Navy jack & ensign (1863 - 65) were almost indistinguishable from the Army's battle flag.
They flew on Confederate Navy ships, but were never used in the slave-trade.
Indeed, perhaps counter-intuitively, the Confederate Constitution also outlawed importing slaves from overseas.

For an example of an actual slave-ship, the Nightingale, when captured off Africa with 961 slaves in April 1861, was then Brazilian owned and had been transporting slaves to Cuba for several years.
And this list of slave-ships seized by Union warships does not suggest any were Confederate ships.

But my point in all this is: the pro-Confederate claim that some slave ships flew the US flag cannot be accurate after 1807, if then, because such ships were outlaws, and when caught were seized, their owners prosecuted.

Here is the second Confederate Naval Jack:

And here, from 1848, USS Jamestown of the Africa Squadron, captured two slave-ships: