It's even a little complicated than that, with a succession of different laws gradually emancipating the slaves. There was some compensation for a while, and different cut-offs for year of birth. The last slaves, in fact, weren't emancipated in New York until 1827, but the slave trade, the legal buying and selling, was outlawed. Of course, after that, and seeing the writing on the wall, slaveowning New Yorkers smuggled their slaves south and sold them for more money than they were going to get through compensation.
All in all, there was plenty of bad behavior to go around, but the original point, that slavery was far from a dying institution and was, in fact, becoming increasingly profitable, still stands.
Oh yes...my point in showing NY State legally allowing slaves into the 1820s (and I trust your date more than mine) was backing up your original contention.
I come to this by way of NYC history. An interesting side note in case you did not know: the slave auctions in NYC were held where Wall St. meets the East River.