I am more knowledgeable about the fall of the Shang dynasty than the Qing. Abolishment of slavery was a centerpiece reform made by the Zhou rulers. Hopefully someone else would have an answer to your question. The Manchu/Jurchens did practice slavery as it was common in the northern steppes to own slaves. Not sure if they kept the practice during the Qing. One could theorize that turkic customs were imported into the empire over the millenia and the laws shifted quite a bit, but I have no evidence nor example to give. Iirc, one of the reasons Genghis Khan declared war on the then Jurchen ruled Jin dynasty was because of rampant slave trade which put many turkic people in bondage in the empire. There were also many Sodgian traders who were famous for introducing slave trade to the then flourishing Tang Dynasty when the culture swinged more liberal and open to foreign culture.