Thomas Jefferson's plan succeeded, though he personally did not free his slaves.

[Union8448]

1. He and his fellow Virginians did limit the spread of slavery. The institution never took root in what was then the Northwest.
2. HIs plan to limit further involuntary immigration of enslaved people was mostly successful. Though in the far south more enslaved people from Africa and the Caribbean were added, legally before 1807, and many covertly after that date. That did make Americanized slaves in the border states more valuable.
3. Personally, he did arrange for Sally Hemmings to be free after he died. And her children, who could pass for white, also were freed. Jefferson's debts probably restricted his ability to free any other slaves. He owed too much money to dispose of the enslaved people who made up part of his collateral.
In time, the Great Lake states were vital to the US in the Civil War. And the size of the enslaved population in the middle 8 states weakened the institution there.

 

[5fish]

Maybe because Black people were not welcomed in Ohio... On slavery but no black people either... @O' Be Joyful

https://www.starbeacon.com/news/slavery-in-ohio/article_b0335730-1854-11ea-aca3-9fa5261b80d2.html

Slavery was abolished in Ohio in 1802 by the state's original constitution. But at the same time, Ohio, with slave-state Kentucky across the Ohio River, took the lead in aggressively barring black immigration.

Black Laws of 1804 and 1807 - Wikipedia

en.wikipedia.org

Ohio's 1803 Constitution continued the Northwest Ordinance's prohibition of slavery north of the Ohio River. Many Ohioans had come from Southern states that allowed slavery and were not willing to grant rights to African Americans.[1]

Jun. 30, 1829 | Cincinnati, Ohio, Forces Hundreds of Black People to Leave

Learn more about our history of racial injustice.

calendar.eji.org

On June 30, 1829, officials in Cincinnati, Ohio, issued a notice requiring Black residents to adhere to laws passed in 1804 and 1807 aimed at preventing “fugitive slaves” and freed Black people from settling in Ohio, which forced hundreds of Black people to flee.

 

[5fish]

Michigan was a little different...

History of slavery in Michigan - Wikipedia

en.wikipedia.org

Slavery in Michigan began centuries ago with the French when they began to trade with indigenous people in the 16th century. Detroit was founded at the beginning of the 18th century, at which point the number of enslaved people began to be recorded. While the records are incomplete and therefore under-report the numbers, historian Marcel Trudel counted 523 Native American and 127 Black enslaved people, for a total of 650 people, from the 18th and early 19th century Detroit.[1] The average life-span for enslaved Native Americans was 17.2 years, for Blacks, the average life span was 25.2 years.[1]

About 10% of early Detroit's population was made up of indentured servants, who worked for five to seven years paying off the cost of their transportation to the New World or debts. Although they were free, their contracts could be bought and sold.[

Detroit Built with Slaves...

Another city, Detroit with a past stained by slavery in it founding and early years... It started under the French , the English and with early America. It a long article but goes in some detail so read the link...

www.jggscivilwartalk.online

 

[5fish]

 

[5fish]

The truth is Jefferson's plan worked in the end for slavery was pushed out of the Northwest Territories but not for slavery trying to get its claws in there...

William Henry Harrison most likely posed the greatest threat to allowing slavery in the territories...

History of slavery in Indiana - Wikipedia

en.wikipedia.org

.
Indiana courts never ruled on the Ordinance/slavery issue during the territorial period. When the issue of slavery was in the courts, it "was always treated as an existing institution and its legality went unchallenged."[20][21] Early Hoosiers, including William Henry Harrison, wanted to have slavery legalized in the new territory. Harrison may have been motivated by the need to appease existing slaveowners, the need for labor in a developing territory, or the desire to attract immigrants from southern colonies.[19] They sought passage of a new law to override the Northwest Ordinance's ban on slavery. Harrison succeeded in getting permission from Congress for the territory to decide for itself whether slavery should be legalized. Harrison and his party sought to gradually legalize slavery three times (1803, 1807, and 1809) but all three efforts ultimately failed.[22][23] Harrison succeeded, however, in passing laws that established forms of indentured servitude.[24]

Harrison was particularly interested in having slavery legalized. He maintained a plantation style home in Vincennes called Grouseland. Harrison was also in the process of constructing another plantation style farm called Harrison Valley near Corydon in 1807, the same year he was pushing for slavery to be legalized.[25]