Good question.

Most likely it means that stem cell therapies for PCS sufferers are improbable.

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The simple need for the damaged neuron rescue type of stem cell therapy to take place while the damaged cells are still alive makes this therapeutic window very short.

The scientists had hoped that the stem cells would identify the surrounding cell's instructions and adapt to them, thus becoming the specialized neural cell needed at that specific location. When they discovered that this does not happen, they had to look to other ways to 'repair' damaged neuronal cells rather than 'grow' new neurons.

Maybe there will come a day when any head injury is immediately treated with a stem cell cocktail that can rescue the damaged cells.

This will mean that only the damaged cells can be repaired. The cells that have died or are beyond rescue will likely be lost permanently.

This still leaves some hope for Parkinson's and Alzheimer's since those diseases start with weakened and damaged cells. Hopefully, those cells can be rescued.

This brings to mind the philosophical question: Where does the soul and/or emotional mind reside? Is it limited in its ability to recover/grow/heal?