I don't know about the real aircraft but the 737 Classic simulator will execute a perfectly respectable smooth coupled landing just on one autopilot. Under this one autopilot operation there is definately no autotrim back at 400RA though, nor at any other stage. It is comforting to have that fall back availibility on one autopilot if you do not have a second autopilot available for some reason and you just have to get in in bad weather on the ILS.