Which accomplishment was the northwest ordinance unable to achieve

The Northwest Ordinance - also called Ordinance of 1787 - was an Act of the Congress that created the Northwest Territory. It established legal basis of land ownership, abolition, and transfer of state claims, admission of new states, education, the establishment of territorial government, established natural rights, prohibition of slavery and effect of the act on native Americans.

The problem was that the Ordinance had no effect on slavery. The states formed out of the territory did not become free by virtue of the Ordinance nor in consequence of it. They became free because they wanted to and recorded laws by themselves.