Let me rephrase your question. Only 10% of the axons in the spinal cord are necessary and sufficient for recovery of functions such as locomotion. That is probably why a majority of people with so-called "incomplete" spinal cord injury recover walking. As many as 50% of people with incomplete spinal cord injuries will recover walking.

Many people may have 5% or 8% of the axons and are not functioning. For such people, preserving, restoring, or regrowing 2-5% of the axons may restore substantial function. I have seen people who can walk so normally that most people would not know that they had spinal cord injury if they saw them. However, such people will tell you that it is not exactly the same as it was before they were injured. They may not be as well coordinated and may not be able to perform as well but function is function. The answer to your question is of course that 100% of the spinal cord will be necessary for 100% of the function. But 10% of the connection can mediate substantial function.