Dave,
In reality you should upgrade all your equipment to the latest revisions, mismatching them can lead to some unexpected problems. A while back I had a run away Train on my 3rd level, because of a mismatched Hand held Remote Control and TIU, after Barry advised me to make sure all my DCS equipment was matched, and to the latest revision if possible, I eliminated the problem. Some unexpected crazy control problems can happen when you mismatch your DCS Packages.
PCRR/Dave