The June 2016 737CL FCTM changes the pattern to say:
Before starting the turn to base leg, extend the landing gear, select flaps 15,
Turning base leg, adjust thrust as required while descending at approximately 600-700 fpm.
Extend landing flaps before turning final.
I understand that for the B737NG equivalent pattern, landing flaps are selected before turning base and then the landing checklist is called.
I don't understand your question. Your conclusions seem to contradict what you have already posted from FCTM.