I am guessing that the RGS continued to use the DRGW (1924?) Rule Book for awhile before adopting the new DRGW 1938 Rule Book. The 1938 Rule Book discontinued the use of the center marker on the rear of trains. The RGS published a new Timetable on June 11, 1939. Like most railroads, sometimes communication was poor. I bet there is a RGS General Order out there somewhere that clarifies the adoption of the 1938 DRGW Rule Book.
I believe that the 1938 Rule Book also was the beginning of the change from the use of green lenses on the markers to the yellow lenses. This conversion took took some time as well and continued well into the fall of 1939.It probably took the RGS some time to make this conversion as well.
MD Ramsey