If that were so then the southern states must have just been swimming in free blacks. But a check of the census records shows that just wasn't so. Alabama had 438,000 black persons, 99.4% of whom were slaves. Mississippi had 773 free blacks, down from the 1850 census. Arkansas had 144, also down from the prior census. Louisiana had more free blacks in 1830, over 25,000, than they had in 1860, less than 19,000. If manumission were as free and open as you claim then these figures couldn't be true.
http://www.press.uillinois.edu/epub/books/schweninger/s4.html
Read # 67. This is the family that I was referencing when I was talking about black planters in the NE part of the county.