Well, that link was very informative in a number of areas; unfortunately it did not answer directly my original question, and in fact encumbered it with a bit more confusion. Rather than being completely ineffectual, the Slave Import Ban of 1808 seems to have had the effect of making slaves much more valuable in 1860 than in 1810, so it must have had SOME teeth. So again, I must ask how the slave population managed to triple in two generations. Any takers?