B737-300 autoland on one autopilot
Some years ago, a Boeing instructor pilot told me the 737-300 does a perfectly satisfactory autoland on one autopilot except there is no stabiliser back trimming at 400 ft. Have since seen this demonstrated many times in the 737-300 simulator and it works nicely even though no stab trim operation at 400 ft. The flare is perfect.
What is the purpose therefore of the stab trim winding back at 400 ft RA on a two autopilot autoland when it doesn't happen on a single pilot autoland?