It sounds like your unit is either small enough that you get daily contact with CO, or you fill in a position that the CO interacts with you on a regular basis. In my unit, the CO wouldn't know if a member wants to be accommodated retained unless he is notified of such, which in our unit, plus many others, is in the form of a memo. Also, the representation is not strictly to offer remarks regarding the medical issue. It is to provide input to anything regarding the process (proposed release date, perception of bias in the process, etc. etc.).
I find it odd that the CO had to make a specific reference in his letter to DMCA, as the 2088 should/could have included his recommendation for retention.