I just noticed that ISNCSCI practice 3 has the same concept. Someone posted a question to the forum about the motor level in this case about a month ago, and Chrissy’s explanation is very helpful:
“even if motor scores are normal in all testable regions, if sensation is impaired between T2 and L1, the motor level is the lowest level with intact sensation.” The ASIA is purposefully designed to make conservative assumptions if there are unknowns.
I had the exact same question, thanks for posting! I think you’re right that even though the motor levels are intact all the way to S1, we can’t assume that they are intact in the areas that don’t have myotomes (T2-L1) because sensation is not intact there. So the lowest motor level we can say with confidence is intact is T1. BUT like you said, if sensory was intact all the way down, then the motor level would be S1. Or if sensory was intact to T3, for example, then the motor level would also be T3. Does this sound right?