Slavery in the United States

First, I would dispute your assertion that slaves were being freed from 1775 to 1830. While slavery might have been stagnant from 1775 to the 1790s, slaves were not being freed. Slavery was just not expanding. Now, we may be having a semantic argument, as you use the word "many", and my opinion is that only a few slaves, in relation to the hundreds of thousands, about 500,000 by 1800, of slaves in the U.S. were freed after the Revolutionary War. And it also may be that you are looking at mostly Northern states where slavery never really took root. Northern states, which are in colder climates and in more mountainous regions, were never suited for the plantation-style slavery that took root in the South. And, after the Revolutionary War, many of these states abolished slavery during this period. But, again, these freed slaves were only a small minority of slaves held in the United States as the primary slave-holding area was the South and not the Northern states that abolished slavery.

Also, another way to freedom was escape. Slaves in the South, particularly Mississippi, Louisiana, Alabama and Georgia could escape south to Spanish Florida prior to 1819, the year that Andrew Jackson conquered the state and forced the Spanish to sell it to the U.S. Slaves could also escape north along the Underground Railway into free states and Canada until the Civil War. However, the Fugitive Slave Act of 1851 and the Dred Scott decision handed down by the Supreme Court in 1857 made escape to the North problematic. Even longtime abolitionist Frederick Douglas, himself an escaped slave, went on a speaking tour of Europe during this time period to avoid being re-enslaved. Although tens of thousands of slaves made their way north, escapees were still a small percentage of the overall slave population in any given year.

So it may be semantic, but I question if "many" slaves, at least in relation to the total slave population in the United States, were freed during the time period