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.