Thanks for this question! The minimal detectable change (MDC) is the minimum amount of change in a score to be confident the change is not due to measurement error. While we may not expect a change in neurologic level of injury or AIS grade in chronic SCI, it is very likely a patient will have repeat ISNCSCIs performed over their lifetime of care and (in my experience) patients may report subjective change from year to year. It is helpful to have know the values for which we can confidently say real change has or has not occurred.
Here is an excerpt from the Marino article (https://pubmed.ncbi.nlm.nih.gov/18581663/):
We have estimated the magnitude of difference in scores required to represent a true change rather than measurement error. Our results indicate that the scales are very sensitive to change in complete patients but only moderately sensitive in incomplete patients. [Previous studies] looked at agreement for individual sensory points and muscle grades only, not total scores, and found limited agreement among raters. Individual item scores would be expected to have lower reliability and agreement than scale scores, because random error tends to cancel out in the total scores. We agree that one should not place much importance in changes of an individual sensory score or in small changes in a muscle grade.