Mike Alexander and I were out at the UM's Bentley Historical Library this afternoon. They have paper copies of the MTS documentation from March 1967 and June 1967 (Box 12, UM Computing Center Publications). MTS had more features in those very early days before virtual memory support than Mike remembered.
The March 1967 version was a collection of ditto sheets that appear to have been written incrementally over time with different dates for different sections. The earliest is dated November 1966 and latest is dated March 1967. The June 1967 version was mimeographed or something similar and is probably the "first edition". Both were a single "volume". The third version (second edition) from December 1967 was two volumes. The third version (second edition) is the first one for which there is a digital copy.
In March and in June 1967 the name used in the documentation was "MTS: UMMPS Terminal System". It wasn't until the second edition in December 1967 that "MTS: Michigan Terminal System" appeared.